Rotary-linear actuation assembly

Abstract

A rotary-linear actuation assembly comprising a casing internally housing an output shaft arranged coaxial with an actuation axis (A) in a translationally and rotationally movable manner, at least two actuators, of which a first actuator is adapted to impose a translational movement along the actuation axis (A) on the output shaft and a second actuator is adapted to impose a rotary movement about the actuation axis (A) on the output shaft, and at least one position sensor adapted to detect an instant position of the output shaft inside the casing. At least one position sensor is mounted in fixed manner in respect of rotation about the actuation axis (A) and in fixed manner in respect of translation along the actuation axis (A) and faces at least a portion of the output shaft.

Claims

1. A rotary-linear actuation assembly (10, 110) comprising a casing (25, 125) with which there are associated: an output shaft (14, 113) arranged coaxial with an actuation axis (A) in a translationally and rotationally movable manner; at least two actuators, of which a first actuator (11, 111) is adapted to impart a translational movement along the actuation axis (A) on the output shaft (14, 113) and a second actuator (12, 112) is adapted to impart a rotary movement around the actuation axis (A) on the output shaft (14, 113); and at least one position sensor (30, 130) adapted to detect an instant position of the output shaft (14, 113) inside the casing (25, 125); wherein said at least one position sensor (30, 130) is mounted in a rotationally fixed manner about the actuation axis (A) and in a translationally fixed manner along the actuation axis (A), and faces at least a portion (14b, 113a) of the output shaft (14, 113), wherein the at least a portion (14b, 113a) of the output shaft (14, 113) bears, on an outer surface thereof, a two-dimensional mark (31, 131) that extends over at least an angular portion around the output shaft (14, 113) and at least an axial section along an axial extension of the output shaft (14, 113), wherein said at least one position sensor (30, 130) includes a single stationary sensor that detects both an instant axial position and an instant angular position of the output shaft, wherein the stationary sensor is an optical sensor and comprises a laser source emitting a light beam (32) aligned to impinge on the at least a portion (14b, 113a) of the output shaft that bears the two-dimensional mark (31, 131), and a photodetector toward which a return beam (33) is reflected, and wherein the two-dimensional mark (31, 131) comprises a plurality of areas (40), and each of the areas (40) comprises invariable markers (41) defining at least one of the contour and center thereof and acting as references.

2. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the two-dimensional mark (31, 131) extends substantially all around the output shaft (14, 113).

3. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the two-dimensional mark (31, 131) axially extends along the output shaft (14, 113) over at least a length substantially corresponding to a maximum stroke travelled by the output shaft (14, 113) under action imparted by the first actuator (11, 111).

4. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the outer surface of the at least a portion (14b, 113a) of the output shaft (14, 113) bearing the two-dimensional mark (31, 131) is a head surface of the output shaft (14, 113).

5. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the two-dimensional mark (31) comprises a plurality of markers (42, 43, 44) variable along at least one of an angular extension and the axial extension of the at least a portion (14b, 113a) of the output shaft (14, 113) bearing the two-dimensional mark (31).

6. The rotary-linear actuation assembly (10, 110) according to claim 5, wherein the invariable markers (41) and the plurality of markers (42, 43, 44) comprise a plurality of subareas of the outer surface of the at least a portion (14b, 113a) of the output shaft (14, 113) having respectively different opacity degrees.

7. The rotary-linear actuation assembly (10, 110) according to claim 6, wherein the photodetector includes a CCD or a CMOS.

8. The rotary-linear actuation assembly (10, 110) according to claim 5, wherein the invariable markers (41) and the plurality of markers (42, 43, 44) comprise a plurality of magnetic tracks obtained on the outer surface of the at least a portion (14b, 113a) of the output shaft (14, 113) and the at least one position sensor (30) comprises an array of magnetic sensors.

9. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the first (111) and the second (112) actuators are arranged in a mutually coaxial and concentric manner, the two-dimensional mark (131) being obtained on at least a portion of a jacket surface of a magnetic rotor (118) mounted on the output shaft (113) associated with a radially outermost actuator (112) out of the first actuator (111) and the second actuator (112).

10. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein a jacket surface of the at least a portion (14b, 113a) of the output shaft (14, 113) is coated with a coating film (119), the two-dimensional mark (31) being obtained on such a coating film (119).

11. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein the stationary sensor is fixedly mounted in proximity of an electromagnetic stator (16, 116) associated with a radially outermost actuator (112) out of the first actuator (111) and the second actuator (112).

12. The rotary-linear actuation assembly (10, 110) according to claim 1, wherein each of the areas (40) further comprises first variable markers (42) adapted to indicate the angular position of the area, second variable markers (43) adapted to indicate a longitudinal position of the area, and additional markers (44) adapted to provide a code for error check and correction of a content of the area.

13. The rotary-linear actuation assembly (10, 110) according to claim 12, wherein said markers (41, 42, 43, 44) can be identified in a set of subareas, the whole of the subareas of all markers relevant to a specific area (40) forming the area itself.

Description

(1) In the drawings:

(2) FIG. 1 is a sectional view of a first preferred embodiment of the rotary-linear actuation assembly according to the present invention, in a working configuration;

(3) FIG. 2 is a sectional perspective view of a second preferred embodiment of the rotary-linear actuation assembly according to the present invention, in a working configuration;

(4) FIG. 2a is an enlarged detail of FIG. 2;

(5) FIGS. 3 and 3a are schematic representations of a first position sensor employed in a rotary-linear actuation assembly according to the present invention and of an exemplary mark to be used with such a first position sensor, respectively;

(6) FIGS. 4 and 4a are schematic representations of a second position sensor employed in a rotary-linear actuation assembly according to the present invention and of an exemplary mark to be used with such a second position sensor, respectively.

(7) In the following description, for explaining the Figures, the same reference numerals are used to denote constructive elements having the same functions. Moreover, for the sake of clarity of the illustration, it is possible that some reference numerals are not shown in all Figures.

(8) Indications such as “vertical” and “horizontal”, “upper” and “lower” (in the absence of further indications) are to be intended with reference to the mounting (or operating) conditions and with reference to the normal terminology in use in the current language, where “vertical” denotes a direction substantially parallel to the direction of the vector force of gravity “g” and “horizontal” denotes a direction perpendicular thereto.

(9) Referring to FIG. 1, there is shown a first preferred embodiment of a rotary-linear actuation assembly according to the present invention, generally indicated by reference numeral 10.

(10) Rotary-linear actuation assembly 10 comprises a casing 25 inside which two actuators 11, 12 are housed, of which a first actuator, or linear actuator 11, is adapted to provide, at the output from actuation assembly 10, a translational movement along a main actuation axis A, and a second actuator, or rotary actuator 12, is adapted to provide, at its output, a rotary movement about actuation axis A.

(11) Each actuator 11, 12 is an electromagnetic actuator and acts on a respective shaft 13, 14 arranged coaxial with actuation axis A. To this end, each actuator 11, 12 includes a respective electromagnetic stator 15, 16 integral with casing 25 and cooperating with a corresponding magnetic rotor 17, 18, integrally carried by the corresponding shaft 13, 14.

(12) Shafts 13, 14 of the two actuators are arranged one above the other and are mutually connected through a rotation-decoupling joint 20. More particularly, lowermost shaft 14 is the output shaft of actuation assembly 10.

(13) More particularly, shaft 13 of the first actuator 11, or first shaft 13, includes an outer tubular body 22, with axis parallel to actuation axis A, fixedly connected to a coaxial nut member 19 having an internal thread. The first shaft 13 further includes a recirculating ball screw 21 housed within outer tubular body 22 and coupled with nut member 19 in such a manner that a rotation of nut member 19 causes a translation of recirculating ball screw 21.

(14) Recirculating ball screw 21 is connected at its bottom end to rotation-decoupling joint 20, which is to make rotation of the first shaft 13 independent of shaft 14 of the second actuator 12, or second shaft 14 or output shaft 14.

(15) More specifically, decoupling joint 20 is adapted to allow a relative rotation between the second shaft 14 and recirculating ball screw 21 of the first shaft, and is moreover adapted to connect coaxial shafts 13, 14 so as to prevent a relative translation thereof. This is necessary in order to provide at the output the linear position control imposed by the first actuator 11.

(16) The second shaft 14 is connected at its upper end to rotation-decoupling joint 20 and it has a first portion 14a on which magnetic rotor 18 coupled with electromagnetic stator 16 of the second actuator 12 is fixedly mounted. Magnetic rotor 18 has an axial size larger than the axial size of stator 15, so that stator 16 always at least partly faces rotor 18 independently of the axial position taken by the latter.

(17) According to the embodiment shown in FIG. 1, a mark 31, schematically shown in FIG. 3, is formed at least on a second portion 14b of the outer jacket surface of the second shaft 14. Such a mark extends all around shaft 14 and axially extends along shaft 14 over at least a length substantially corresponding to the maximum stroke shaft 14 can travel under the action imparted by the first actuator 11.

(18) Moreover, a position sensor 30 is provided, which is arranged in a rotationally and translationally fixed manner relative to axis A in correspondence of shaft portion 14b bearing mark 31 and which faces the latter.

(19) Referring in particular to the embodiment shown in FIG. 1, position sensor 30 is an optical sensor and is located directly below electromagnetic stator 16 of the second actuator 12.

(20) In FIG. 2, there is shown a second preferred embodiment of a rotary-linear actuation assembly according to the present invention, generally indicated by reference numeral 110.

(21) Rotary-linear actuation assembly 110 comprises a casing 125 inside which two actuators 111, 112 are housed, of which a first actuator, or linear actuator 111, is adapted to provide, at the output from actuation assembly 110, a translational movement along a main actuation axis A, and a second actuator, or rotary actuator 112, is adapted to provide, at its output, a rotary movement about actuation axis A.

(22) Each actuator 111, 112 is an electromagnetic actuator and both of them act on a same shaft 113 coaxial with actuation axis A.

(23) More particularly, linear actuator 111 is adapted to impart a translational displacement between a first end-of-stroke position, in which output shaft 113 is substantially wholly received within casing 125 or projects therefrom by a minimum length, and a second end-of-stroke position, or position of maximum projection of output shaft 113 from casing 125.

(24) Each actuator 111, 112 includes a respective electromagnetic stator 115, 116 cooperating with a corresponding magnetic rotor 117, 118, both magnetic rotors 117, 118 being constrained to displace with output shaft 113. Moreover, actuators 111, 112 are coaxially and concentrically arranged.

(25) According to the embodiment shown in FIG. 2, a mark 131, shown in detail in FIG. 2a, is formed on at least a portion 113a of the outer jacket surface of output shaft 113. Such a mark extends all around shaft 113 and axially extends along shaft 113 over at least a length corresponding to the maximum stroke the shaft can travel under the action imparted by linear actuator 111.

(26) Specifically, in the embodiment shown in FIG. 2, mark 131 is formed on the jacket surface of radially outermost magnetic rotor 118 mounted on output shaft 113. More particularly, mark 131 is formed on a coating film 119 coating the outer surface of radially outermost magnetic rotor 118.

(27) Moreover, a position sensor 130 is provided, which is arranged in stationary manner in correspondence of portion 113a of output shaft 113 bearing mark 131 and which faces the latter. Referring in particular to the embodiment shown in FIG. 2, position sensor 130 is an optical sensor and is located directly above outermost electromagnetic stator 116.

(28) According to alternative embodiments (not shown), the position sensor is a magnetic sensor and the second portion 14b, 113a of the outer surface of output shaft 14, 113 on which mark 31, 131 is formed does not overlap magnetic rotor 118, 118, but it is confined above or below the same. Also in this case position sensor 30, 130 is located so as to at least partly face such a portion bearing mark 31, 131.

(29) In the schematic representation shown in FIG. 3, position sensor 30, 130 is an optical sensor and comprises a laser source emitting a light beam 32 impinging on shaft portion 14b, 113a bearing mark 31, 131, and a photodetector, e.g. a CCD or a CMOS, towards which return beam 33 is reflected.

(30) As shown in FIG. 3a, mark 31, 131 preferably comprises a plurality of areas 40, and each area 40 comprises invariable markers 41 defining the contour and/or the centre thereof and acting as references.

(31) Each area 40 further comprises first variable markers 42 adapted to indicate the angular position of the area, and second variable markers 43 adapted to indicate the longitudinal position of area 40, besides possible additional markers 44 adapted to provide a code for error check and correction of the content of each area 40. Markers 41 to 44 can be identified in a set of subareas, the whole of the subareas of all markers relevant to a specific area 40 forming the area itself.

(32) According to the alternative embodiment shown in FIG. 4, outer surface portion 14b, 113a of output shaft 14, 113 bearing mark 31, 131 is a head portion of output shaft 14, 113, and position sensor 30, 130 is mounted in rotationally and translationally fixed manner relative to axis A so as to at least partly face outer surface portion 14b, 113a bearing mark 31, 131.

(33) FIG. 4a shows, by way of example, an area 40 of a mark 31, 131 borne by the head portion of output shaft 14, 113. Such an area 40 comprises invariable markers 41 acting as references and variable markers 42 adapted to indicate the angular position of the area. Moreover, additional markers 44 are provided, which are adapted to provide a check code for each area 40.

(34) The operation of rotary-linear actuation assembly 10, 110 according to the invention is as follows.

(35) When actuation assembly 10, 110 is operated, output shaft 14, 113 is made to rotate and/or translate depending on the commands given to actuators 11, 12, 111, 112. Consequently, also mark 31, 131 is made to rotate and/or translate, thereby causing a specific area 40 of the mark, or at least a substantial portion of area 40, to face position sensor 30, 130.

(36) Position sensor 30, 130 thus detects markers 41-44 present in the area facing at that moment sensor 30, 130, thereby recognising references 41 of area 40 detected and, based on such references, detecting and recognising variable markers 42, 43 carrying the information about the instant angular and/or longitudinal position of output shaft 14, 113.

(37) In case of an optical sensor 30, 130, the laser source emits a laser light beam impinging on surface portion 14b, 113a bearing mark 31, 131 faced at that moment by the optical sensor. Emitted beam 32 is differently reflected depending on the kind of subarea it meets. For instance, the mark may be formed of alternating glossy and opaque subareas. In this case, laser light beam 32 is reflected or at least partly absorbed, thereby generating a phase variation and a time delay in return beam 33 depending on the finish (glossy or opaque) of the surface portion it impinges on.

(38) Moreover, by taking as reference an invariable marker 41, for instance the marker of the centre of area 40 of mark 31 the optical sensor is facing at that moment, and by comparing two consecutive acquisitions, the photodetector is capable of detecting the displacement of such a marker, and thus of output shaft 14, 113, with extreme precision.

(39) For instance, in case of a CMOS or CCD photodetector, the horizontal and vertical pixels separating the two consecutive measurements corresponding to the specific invariable marker 41 are measured, each pixel corresponding to displacements of the order of the tenths of micron. In this manner, depending on the time elapsed between two consecutive acquisitions, it is also possible to compute the velocity and the acceleration of output shaft 14, 113.

(40) In case of a mark 31, 131 formed on a head portion of output shaft 14, 113, variable markers 42 could even contain only the information about the angular position, since the longitudinal position may be obtained from the return time of the reflected beam, which is proportional to the distance between the head surface bearing mark 31, 131 and the laser source.

(41) In case of use of a magnetic sensor 130, mark 131 comprises a plurality of magnetic tracks and sensor 130 comprises an array of magnetic micro-sensors and is adapted to electrically reproduce the magnetic signals arriving at that array.

(42) The features of the rotary-linear actuation assembly according to the present invention are clearly apparent from the above description, as are clearly apparent the relevant advantages.

(43) Further variants of the embodiments described above are possible without departing from the teaching of the invention.

(44) Lastly, it is clear that a rotary-linear actuation assembly as conceived can undergo several changes and modifications, all included in the invention. Moreover, all details can be replaced by technically equivalent elements. In practice, any material as well as any size can be used, depending on the technical requirements.