Patent Description:
Rotary-linear actuators are currently used in several industrial applications requiring that a same actuator output shaft be capable of imparting in independent manner, either simultaneously or sequentially, both a rotary movement and a linear movement.

In order to precisely and reliably control the motion of the output shaft of such an actuator, it is necessary to be capable of detecting in real time both the instant angular position and the instant longitudinal position taken by the shaft.

Thus, in prior art actuation assemblies, a plurality of sensors are currently used, which are each devoted to detect a specific spatial coordinate taken by the output shaft, in order to obtain the instant position of the same shaft based on which the control of the motor(s) acting on the shaft is to be set.

For instance, in order to detect the angular coordinate of the output shaft, it is known to use an optical or magnetic rotary sensor or, in the alternative, an encoder, an inductive sensor (resolver), a potentiometer or a Hall effect sensor. As to the detection of the axial coordinate of the output shaft, an optical ruler, an optical encoder or an inductive transducer (Inductosyn) are usually employed.

The Applicant has realised that the sensors currently used in rotary-linear actuation assemblies require, for their correct operation, that the movement of the output shaft be at least partly followed. This entails the need for specific movable supports, such as for instance a rotary support following the shaft rotation and carrying the linear position sensor, as well as a support which allows translation of the rotary sensor together with the shaft and on which the sensor is keyed.

Moreover, the Applicant has noticed that mounting the sensors on the proper supports entails not only problems of alignment on the axes, but also the use of translating and rotating fastening means based on bushings and bearings, which determine in any case sliding and/or rolling contacts. This not only increases the number of elements that can be subjected to wear in the actuation assembly, but may also give rise in time to lack of precision in the movement alignment of the sensors with the shaft and hence to lack of precision in the detection, thereby requiring a constant maintenance in order to ensure in time a proper sensor operation and hence a good measurement precision.

<CIT> discloses a roto-translating drive unit for a printing machine provided with drive motors for separate rotary and linear driving each provided with corresponding set of permanent magnets. <CIT> discloses a roto-translating drive unit for machine tools in general. <CIT> discloses a single stationary sensor for detecting both the instant axial position and instant angular position of a roto-translating shaft. <CIT> discloses an electric motor combination for simultaneous rotary and linear movement, having two separate primary parts acting as stators and common rotor.

<CIT> discloses a method to determine displacement, axial and radial in a rotating component, wherein an optical displacement probe is used incident upon a target formed from surface features in a rotating component surface. <CIT> an angular and axial position sensor arrangement comprising a coding pattern composed of values along their circumference to determine angular position by some sensors overlapping them.

The problem upon which the present invention is based is thus to provide a rotary-linear actuation assembly which is capable of overcoming the limits of the state of the art in simple, reliable and cheap manner.

Within such a problem, it is an object of the present invention to conceive a rotary-linear actuation assembly equipped with a displacement sensor which is capable of correctly detecting both the angular displacement and the linear displacement of an element movable according to a roto-translational movement, without using movable supports following at least partly the roto-translational movement of the movable element.

More particularly, it is a further object of the present invention to provide a rotary-linear actuation assembly which is capable of ensuring a high operation precision and of maintaining such a precision in reliable manner in time, while demanding a minimum engagement in terms of maintenance and setting.

In accordance with a first aspect thereof, the present invention therefore concerns a rotary-linear actuation assembly according to claim <NUM> comprising a casing internally housing:.

and wherein the at least one position sensor is mounted in fixed manner in respect of rotation about the actuation axis and in fixed manner in respect of translation along the actuation axis, and faces at least a portion of the output shaft.

Advantageously, in this manner, equipping the actuation assembly with movable supports and the associated transmission members, such as for instance splined members or recirculating rolling screws, is no longer necessary, thereby reducing the overall complexity of the assembly as well as the need for maintenance thereof.

According to the invention, the at least a portion of the output shaft bears, on the jacket surface thereof, a mark extending over at least an angular portion around the output shaft and/or over at least an axial section along the axial extension of the output shaft.

Advantageously, it is thus possible to have the information about the instant position of the output shaft directly on the surface thereof, thus enabling working with a single sensor, which moreover is stationary as far as the displacements of the output shaft are concerned.

The present invention may have at least one of the following preferred features, which in particular can be combined together at will in order to cope with specific application requirements.

The mark extends substantially all around the output shaft.

The mark axially extends along the output shaft over at least a length substantially corresponding to a maximum stroke travelled by the output shaft under the action imparted by the first actuator.

The mark comprises a plurality of variable markers along the angular and/or axial extension of the output shaft portion bearing the mark.

Conveniently, it is thus possible to have available two-dimensional information about the instant position of the shaft, which information can be detected by the stationary sensor. It is thus possible to simultaneously detect both the instant axial position and the instant angular position of the shaft by means of a single stationary sensor.

Even more preferably, the markers comprise a plurality of subareas of the surface of the output shaft portion having respectively different opacity degrees.

The mark is divided into a plurality of areas each comprising a set of subareas forming the markers relevant to a given angular and axial position.

More preferably, the areas into which the mark is divided are polygonal, preferably square, hexagonal or octagonal.

The position sensor comprises at least one light source, preferably a laser light source, and at least one photodetector, preferably a CCD or a CMOS.

The first and the second actuator are arranged in a mutually coaxial and concentric manner, the mark being formed on at least a portion of a jacket surface of a magnetic rotor mounted on an outer jacket surface of the output shaft and associated with a radially outermost actuator out of the first and the second actuator.

In the present description and in the claims that follow, the term "magnetic rotor" denotes both a rotor of a kind with permanent magnets and a ferromagnetic rotor having a configuration suitable to transfer a rotation torque.

Preferably, the jacket surface of the at least a portion of the output shaft is coated with a coating film, the mark being formed on such a coating film.

Preferably, the position sensor is fixedly mounted in an axial position in close proximity of an electromagnetic stator associated with a radially outermost actuator out of the first and the second actuator.

More preferably, the radially outermost actuator is the second actuator adapted to impose a rotary movement about the actuation axis on the output shaft.

In the alternative, the radially outermost actuator is the first actuator adapted to impose a translational displacement along the actuation axis on the output shaft.

Preferably, the first and the second actuator are arranged axially side by side and are mutually connected by at least one rotation-decoupling joint, the output shaft carrying a magnetic rotor associated with the second actuator.

More preferably, the position sensor is fixedly mounted in an axial position in close proximity of an electromagnetic stator associated with the second actuator.

Further features and advantages of the present invention will become more apparent from the following detailed description of some preferred embodiments thereof, made with reference to the accompanying drawings.

The different features in the individual configurations can be combined together at will according the preceding description, should the advantages specifically resulting from a particular combination have to be exploited.

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.

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.

Referring to <FIG>, there is shown a rotary-linear actuation assembly which is not part of the present invention, generally indicated by reference numeral <NUM>.

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

Each actuator <NUM>, <NUM> is an electromagnetic actuator and acts on a respective shaft <NUM>, <NUM> arranged coaxial with actuation axis A. To this end, each actuator <NUM>, <NUM> includes a respective electromagnetic stator <NUM>, <NUM> integral with casing <NUM> and cooperating with a corresponding magnetic rotor <NUM>, <NUM>, integrally carried by the corresponding shaft <NUM>, <NUM>.

Shafts <NUM>, <NUM> of the two actuators are arranged one above the other and are mutually connected through a rotation-decoupling joint <NUM>. More particularly, lowermost shaft <NUM> is the output shaft of actuation assembly <NUM>.

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

Recirculating ball screw <NUM> is connected at its bottom end to rotation-decoupling joint <NUM>, which is to make rotation of the first shaft <NUM> independent of shaft <NUM> of the second actuator <NUM>, or second shaft <NUM> or output shaft <NUM>.

More specifically, decoupling j oint <NUM> is adapted to allow a relative rotation between the second shaft <NUM> and recirculating ball screw <NUM> of the first shaft, and is moreover adapted to connect coaxial shafts <NUM>, <NUM> 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 <NUM>.

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

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

Moreover, a position sensor <NUM> is provided, which is arranged in a rotationally and translationally fixed manner relative to axis A in correspondence of shaft portion 14b bearing mark <NUM> and which faces the latter.

Referring in particular to the embodiment shown in <FIG>, position sensor <NUM> is an optical sensor and is located directly below electromagnetic stator <NUM> of the second actuator <NUM>.

In <FIG>, there is shown a second preferred embodiment of a rotary-linear actuation assembly according to the present invention, generally indicated by reference numeral <NUM>.

Each actuator <NUM>, <NUM> is an electromagnetic actuator and both of them act on a same shaft <NUM> coaxial with actuation axis A.

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

Each actuator <NUM>, <NUM> includes a respective electromagnetic stator <NUM>, <NUM> cooperating with a corresponding magnetic rotor <NUM>, <NUM>, both magnetic rotors <NUM>, <NUM> being constrained to displace with output shaft <NUM>. Moreover, actuators <NUM>, <NUM> are coaxially and concentrically arranged.

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

Specifically, in the embodiment shown in <FIG>, mark <NUM> is formed on the jacket surface of radially outermost magnetic rotor <NUM> mounted on output shaft <NUM>. More particularly, mark <NUM> is formed on a coating film <NUM> coating the outer surface of radially outermost magnetic rotor <NUM>,
Moreover, a position sensor <NUM> is provided, which is arranged in stationary manner in correspondence of portion 113a of output shaft <NUM> bearing mark <NUM> and which faces the latter. Referring in particular to the embodiment shown in <FIG>, position sensor <NUM> is an optical sensor and is located directly above outermost electromagnetic stator <NUM>.

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 <NUM>, <NUM> on which mark <NUM>, <NUM> is formed does not overlap magnetic rotor <NUM>, <NUM>, but it is confined above or below the same. Also in this case position sensor <NUM>, <NUM> is located so as to at least partly face such a portion bearing mark <NUM>, <NUM>.

In the schematic representation shown in <FIG>, position sensor <NUM>, <NUM> is an optical sensor and comprises a laser source emitting a light beam <NUM> impinging on shaft portion 14b, 113a bearing mark <NUM>, <NUM>, and a photodetector, e.g. a CCD or a CMOS, towards which return beam <NUM> is reflected.

As shown in <FIG>, mark <NUM>, <NUM> preferably comprises a plurality of areas <NUM>, and each area <NUM> comprises invariable markers <NUM> defining the contour and/or the centre thereof and acting as references.

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

According to <FIG> which discloses an example which is not part of the invention, outer surface portion 14b, 113a of output shaft <NUM>, <NUM> bearing mark <NUM>, <NUM> is a head portion of output shaft <NUM>, <NUM>, and position sensor <NUM>, <NUM> 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 <NUM>, <NUM>.

<FIG> shows, by way of example, an area <NUM> of a mark <NUM>, <NUM> borne by the head portion of output shaft <NUM>, <NUM>. Such an area <NUM> comprises invariable markers <NUM> acting as references and variable markers <NUM> adapted to indicate the angular position of the area. Moreover, additional markers <NUM> are provided, which are adapted to provide a check code for each area <NUM>.

In this case of a mark <NUM>, <NUM> formed on a head portion of output shaft <NUM>, <NUM>, variable markers <NUM> 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 <NUM>, <NUM> and the laser source.

The operation of rotary-linear actuation assembly <NUM>, <NUM> according to the invention is as follows.

When actuation assembly <NUM>, <NUM> is operated, output shaft <NUM>, <NUM> is made to rotate and/or translate depending on the commands given to actuators <NUM>, <NUM>, <NUM>, <NUM>. Consequently, also mark <NUM>, <NUM> is made to rotate and/or translate, thereby causing a specific area <NUM> of the mark, or at least a substantial portion of area <NUM>, to face position sensor <NUM>, <NUM>.

Position sensor <NUM>, <NUM> thus detects markers <NUM> - <NUM> present in the area facing at that moment sensor <NUM>, <NUM>, thereby recognising references <NUM> of area <NUM> detected and, based on such references, detecting and recognising variable markers <NUM>, <NUM> carrying the information about the instant angular and/or longitudinal position of output shaft <NUM>, <NUM>.

In case of an optical sensor <NUM>, <NUM>, the laser source emits a laser light beam impinging on surface portion 14b, 113a bearing mark <NUM>, <NUM> faced at that moment by the optical sensor. Emitted beam <NUM> 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 <NUM> is reflected or at least partly absorbed, thereby generating a phase variation and a time delay in return beam <NUM> depending on the finish (glossy or opaque) of the surface portion it impinges on.

Moreover, by taking as reference an invariable marker <NUM>, for instance the marker of the centre of area <NUM> of mark <NUM> 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 <NUM>, <NUM>, with extreme precision.

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 <NUM> 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 <NUM>, <NUM>.

In case of use of a magnetic sensor <NUM>, mark <NUM> comprises a plurality of magnetic tracks and sensor <NUM> comprises an array of magnetic micro-sensors and is adapted to electrically reproduce the magnetic signals arriving at that array.

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.

Further variants of the embodiments described above are possible without departing from the teaching of the invention defined by the claims.

Lastly, it is clear that a rotary-linear actuation assembly as conceived can undergo several changes and modifications, all included in the invention defined by the claims.

Claim 1:
Rotary-linear actuation assembly (<NUM>, <NUM>) comprising a casing (<NUM>, <NUM>) with which there are associated:
- an output shaft (<NUM>, <NUM>) arranged coaxial with an actuation axis (A) in a translationally and rotationally movable manner;
- at least two actuators, of which a first actuator (<NUM>, <NUM>) is adapted to impart a translational movement along the actuation axis (A) on the output shaft (<NUM>, <NUM>) and a second actuator (<NUM>, <NUM>) is adapted to impart a rotary movement around the actuation axis (A) on the output shaft (<NUM>, <NUM>); and
- at least one position sensor (<NUM>, <NUM>) adapted to detect an instant position of the output shaft (<NUM>, <NUM>) inside the casing (<NUM>, <NUM>) and 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 (<NUM>, <NUM>);
- wherein the at least a portion (14b, 113a) of the output shaft (<NUM>, <NUM>) bears, on the outer surface thereof, a mark (<NUM>, <NUM>) that extends over at least an angular portion around the output shaft (<NUM>, <NUM>) and along the output shaft (<NUM>, <NUM>) over at least a length substantially corresponding to a maximum stroke travelled by the output shaft (<NUM>, <NUM>) under the action imparted by the first actuator (<NUM>, <NUM>);
- wherein the first (<NUM>) and the second (<NUM>) actuator are arranged in a mutually coaxial and concentric manner, the mark (<NUM>) being obtained on at least a portion of a jacket surface of a magnetic rotor (<NUM>) mounted on the output shaft (<NUM>) associated with a radially outermost actuator (<NUM>) out of the first (<NUM>) and the second actuator (<NUM>);
wherein the mark (<NUM>) is formed on the jacket surface of radially outermost magnetic rotor (<NUM>) mounted on output shaft (<NUM>) on a coating film (<NUM>) coating the outer surface of radially outermost magnetic rotor (<NUM>).