Patent Publication Number: US-2022230795-A1

Title: Lvdt with integrated anti-rotation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application No. 21305048.7 filed Jan. 15, 2021, the entire contents of which is incorporated herein by reference. 
     FIELD OF TECHNOLOGY 
     The examples described herein relate to linear variable differential transformers (LVDTs). 
     BACKGROUND 
     LVDTs are a common type of electromechanical transducer that can convert the rectilinear motion of an object to which it is coupled mechanically into a corresponding electrical signal. 
     LVDTs have been widely used in different applications such as in power turbines, hydraulics, aircraft, to name a few. An LVDT functions by converting a position or linear displacement from a mechanical reference (zero or null position) into a proportional electrical signal containing phase (for direction) and amplitude (for distance) information. The LVDT operation does not require an electrical contact between the moving part (probe or core assembly) and the coil assembly, but instead relies on electromagnetic coupling. They may therefore be described as absolute linear position/displacement transducers and are inherently frictionless. 
     SUMMARY 
     An electromechanical actuator is described herein comprising: an actuator rod housed in an actuator housing; a linear variable differential transformer “LVDT” fixed to the actuator housing; an anti-rotation component configured to contact the outer surface of said LVDT; wherein said outer surface of the linear variable differential transformer comprises a first anti-rotation surface feature and wherein said anti-rotation component comprises a second anti-rotation surface feature, and wherein said first and second anti-rotation features are sized and shaped relative to each other such that, when in contact with each other, they are configured to prevent rotation of the actuator rod in use. 
     In some of the examples described herein, the electromechanical actuator may further comprise a motor and a mechanical converter configured to transform torque produced by the motor into linear force applied to said actuator rod. 
     In some of the examples described herein, said anti-rotation component may be positioned between the mechanical converter and the LVDT in use. 
     In some of the examples described herein, the actuator rod comprises a hollow cylindrical region surrounding the LVDT. 
     In some of the examples described herein, said anti-rotation component is positioned between the actuator rod and the linear variable differential transformer in use. 
     In some of the examples described herein, the LVDT extends along a central longitudinal axis X′ between a first longitudinal end and a second longitudinal end. 
     In some of the examples described herein, said anti-rotation surface features may be provided at said first end of the LVDT. 
     In some of the examples described herein, the anti-rotation component may be directly machined onto the inner surface of the actuator rod and be positioned around the external surface of the LVDT. 
     In some examples the anti-rotation surface features may be formed by machining methods. 
     In some of the examples described herein, said anti-rotation surface features may comprise splines, keys or square shaped sections. 
     A method of preventing rotation of an actuator rod in an electromechanical actuator is also described herein comprising: providing said actuator rod housed in an actuator housing; providing a linear variable differential transformer “LVDT” fixed to the actuator housing; providing an anti-rotation component configured to contact the outer surface of said LVDT; providing a first anti-rotation surface feature or features on said outer surface of the linear variable differential transformer and providing a second anti-rotation surface feature or features on said anti-rotation component, and wherein said first and second anti-rotation features are sized and shaped relative to each other such that, when in contact with each other, they are configured to prevent rotation of the actuator rod in use. 
     In some of the examples the method may further comprise providing a motor and a mechanical converter, configured to transform torque produced by the motor into linear force applied to said actuator rod. 
     In some of the examples the method may further comprise positioning said anti-rotation component between the mechanical converter and the LVDT in use. 
     In some of the examples the method may further comprise providing the actuator rod to comprise a hollow cylindrical region surrounding the LVDT. 
     In some of the examples the method may further comprise positioning the anti-rotation component between the actuator rod and the LVDT in use. 
     In some of the examples the anti-rotation surface features are splines, keys or square shaped sections. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  shows a known LVDT in use in an EMA; 
         FIG. 2  shows a new type of LVDT in use in an EMA; 
         FIG. 3  shows the new type of LVDT and an actuator rod; and 
         FIG. 4  shows a mechanical converter and actuator rod. 
     
    
    
     DETAILED DESCRIPTION 
     A known electromechanical actuator (EMA)  10  comprising a linear variable differential transformer (LVDT) sensor  11  is shown in  FIG. 1 . The EMA  10  is electrically powered and is configured to receive a position order from a control computer (not shown). In order to execute this position order, the electrical motor  2  is energised and applies a mechanical torque to the EMA  10 . As the EMA output movement is linear, the rotation of the motor is converted into linear motion by a mechanical converter  19  such as a ballscrew or rollerscrew system. Other means may also be used. As shown in  FIG. 4 , the mechanical converter  19  may comprise a rotational part  4  driven by the motor  2 , converter elements  3  which may be rollers or balls, and a linear output element, which may be considered a separate component to the mechanical actuator  19  and which in the context of this invention is the actuator rod  13 . 
     It can be seen that the LVDT  11  comprises an elongate body having a longitudinal axis X′. In order to stop rotation of the actuator rod  13 , the EMA comprises a separate anti-rotation device  12 . 
     In order to output a purely linear motion of the actuator rod  13 , it is necessary to prevent the rotation of the output of the mechanical converter. In known systems, the rotation of this mechanical converter output is prevented by a dedicated anti-rotation device  12 . In these known linear EMAs, an LVDT  11  is provided as a separate discrete component to the anti-rotation device  12 . The anti-rotation device  12  must be used and located in the same area as the actuator rod  13  and along its axis X′ (which corresponds to the axis X′ of the EMA  10 ). Due to their own design constraints, which are closely related to the functions to be satisfied and technologies, the size of the envelope taken up by both of these components  11 ,  12 , is important. 
     The anti-rotation device  12  comprises a fixed component  15  and a mobile component  16 . The mobile component  16  of the anti-rotation device  12  is attached to an actuator rod  13  and cannot rotate around its own central axis X′, by virtue of coupling with the fixed component  15 , thereby preventing rotational movement. The fixed component  15  of the anti-rotation device  12  is fixed to the actuator housing  1 . The mobile component  16  as shown in  FIG. 1  is positioned between the actuator rod  13  and the fixed anti-rotation component  15 . This mobile anti-rotation component  16  is not fixed relative to the actuator housing  1 , but is instead considered to be a linearly mobile component in use and is attached to the actuator rod  13 . 
     The LVDT  11  also typically has two parts; a mobile component  18 , the LVDT rod, which may include a probe (not shown) and a fixed component, the LVDT body  17 , which may include a coil (not shown). The LVDT fixed part  17  is fixed in place relative to the actuator housing  1  by being attached to the actuator housing. In this configuration, the mobile component of the LVDT  11  can only be displaced linearly inside the LVDT body  17  (fixed part), which itself remains static relative to the actuator housing  1 . The rotation of the mobile component  18  of the LVDT  11  relative to the actuator rod  13  is prevented by fastening elements (not shown) connected to the actuator rod  13  and the rotation of the LVDT body  17 , or fixed component, is prevented by fastening elements (not shown) connected to the actuator housing  1 . Linear motion between both of these parts of the LVDT  11  is generated by motion of the actuator rod  13  in response to the position order as mentioned above. For proper operation of the LVDT  11 , there should be no relative rotational movement between the two components of the LVDT  11 . 
     The fixed component  15  of the anti-rotation device of  FIG. 1  also comprises a hollow cylindrical tube component  15  that is positioned around and contacts the outer circumference of the LVDT body  11  in use. This fixed component  15  of the anti-rotation device  12  is fixed to the outer surface of the LVDT body and to the actuator housing  1 . Both the fixed component  15  of the anti-rotation device  12  and the LVDT body  11  are prevented from rotating with respect to the actuator housing  1  by virtue of being attached to the actuator housing  1 . 
     In order to prevent rotation of the actuator rod  13  in use, the first and second anti-rotation components  15 ,  16  are brought into contact with each other. The rotation is prevented by the corresponding respective shapes of the first and second anti-rotation components  15 ,  16  such as splines, square sections or using additional components such as rollers or balls. 
     The examples described herein aim to provide a new type of LVDT that can be used in an EMA (or other technology) that has a reduced sized envelope. These new examples are related to an anti-rotation feature  160  of the mechanical converter output element (actuator rod  13 ). 
     A new example of an LVDT  21  is shown in  FIG. 2 . As can be seen in this figure, the EMA  100  comprises an LVDT body  27 , the fixed part  27  of the LVDT  21 , that extends along a longitudinal axis X′ which corresponds to the longitudinal axis of the actuator rod  13  and of the EMA  100  itself. This LVDT  21  also includes a mobile rod part  28 . The LVDT body  27  extends between a first longitudinal end  1110  of the LVDT body  27  and a second longitudinal end  1112  of the LVDT body  27 . In this example, the LVDT body  27  remains fixed to the actuator housing  1  as in known systems. 
     The LVDT body  27  outer surface itself comprises an anti-rotation external shape  120  (not shown), or a plurality of anti-rotation external shapes  120 . Examples of such shapes  120  can be splines, keys or square sections. Other than for the addition of this feature, the LVDT  21  does not need to be altered and the LVDT rod  28  is attached to the actuator rod  13  in use, as in known systems. 
     An anti-rotation component  160  is also provided. As shown in  FIG. 3 , the anti-rotation component  160  comprises anti-rotation shapes directly machined onto the inner surface of the output element of the mechanical converter  19 , which in this case is the actuator rod  13 . The anti-rotation shapes  120  provided on the outer surface of the LVDT body  15  are designed and manufactured so as to correspond in shape and size with the shapes provided on the inner surface of the anti-rotation component  160  which surrounds it. Due to this, the anti-rotation shapes  120  provided on the LVDT body  15  in combination with the anti-rotation component  160  on the actuator rod  13  inner diameter are able to prevent rotation by interaction with one another when they come into contact with each other and rotationally lock in place relative to each other. 
     It can be seen, when comparing the known LVDT  11  (which has two anti-rotation components  15 ,  16  surrounding the outer circumference of the LVDT body  17 ) with the new LVDT  21  shown in  FIG. 2  (which only requires one anti-rotation component  160  machined onto the inner surface of the actuator rod  13  to be surrounding the outer circumference of the LVDT body  27  by virtue of having anti-rotation shapes  120  as part of the outer surface of the LVDT body  27  itself rather than such shapes being disposed on a separate component  15  as in the aforementioned known systems), the new LVDT  27  has the advantage that, when used in an EMA, there is a reduced envelope in the actuator rod area. This, in turn, means, for example, if the EMA is provided in the wing of an aircraft, the aircraft wing can also be manufactured to be thinner and lighter. The new LVDTs also provide a reduction in cost as one component is able to provide two functions, both provided by one manufacturer. 
     The examples described herein reduce the overall cost of providing the antirotation function to an EMA and therefore the manufacturing cost of the actuator. As mentioned above, this saving is achieved by no longer having a dedicated component for the anti-rotation function. 
     The bill of material of the actuator is reduced by at least two part numbers and the actuator assembly time is also reduced because there are at least two parts which will no longer need to be mounted. At last, it is expected that only one manufacturer will be able to design and produce that new LVDT with integrated antirotation against at least two different manufacturer with the current design (one for LVDT and other for anti-rotation device). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.