Abstract:
An actuator or servo device comprises an actuator member adapted to move linearly in the motion space of an actuator housing, a microwave position detecting device for detecting the position of the actuator member in the motion space, the actuator member being capable of producing a pressure wave acting on the position detecting device on approaching the position detecting device and a high frequency microwave antenna arrangement for emitting and receiving microwaves, which are at least partially reflected by the actuator member. The actuator device includes dielectric guard cover means, arranged in front of the microwave antenna arrangement. For mechanically uncoupling the guard cover means from the microwave antenna arrangement between the guard cover means and the microwave antenna arrangement a clearance is maintained to allow deformation of the guard cover means thereinto owing to pressure waves.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on European Patent Application No. 05 017 445.7 filed on Aug. 11, 2005, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an actuator or servo device comprising an actuator member adapted to move linearly in the motion space of an actuator housing, a microwave position detecting device for detecting the position of the actuator member in the motion space, the actuator member producing a pressure wave acting on the position detecting device on approaching the position detecting device and a high frequency microwave antenna arrangement for emitting and receiving microwaves, which are at least partially reflected by the actuator member. 
     2. Description of the Related Art 
     Such an actuator is for example described in the German patent publication DE 102 05 904 A1. In this case an actuator device in the form of a pneumatic cylinder with an actuator member is described which is constituted by a piston of the cylinder. The position detecting device comprises a high frequency microwave antenna arrangement for detecting the clearance or, respectively, the position of the piston from an annular abutment, which surrounds the microwave antenna arrangement annularly. On drawing close to the microwave antenna arrangement the piston causes a pressure wave in front of it, which mechanically loads the microwave antenna arrangement and thus for example changes the . position of the microwave antenna arrangement in relation to the housing. Accordingly the clearance measurement signal, which is produced by the position detecting device, is influenced comparatively strongly. Furthermore the measurement-related signal may fail. 
     SUMMARY OF THE INVENTION 
     One object of the invention is hence to design an actuator or servo device of the type initially mentioned so as to be less sensitive to mechanical effects. 
     In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention there is a provision in the case of an actuator device of the type initially mentioned such that it comprises dielectric guard cover means, arranged in front of the microwave antenna arrangement for the mechanical protection of the microwave antenna arrangement and between the guard cover means and the microwave antenna arrangement for mechanically uncoupling the guard cover means from the microwave antenna arrangement a clearance is maintained to allow pressure wave related deformation of the guard cover means into the clearance. 
     By virtue of the guard cover means in accordance with the invention the position of the microwave antenna arrangement remains constant and uninfluenced by thermal and pressure effects or is at least substantially constant. 
     While the guard cover means may deform under the effect of a pressure wave, it remains mechanically separate from the microwave antenna arrangement and conducts any remaining kinetic energy of the actuator member, as for instance the piston of a pneumatic cylinder, into the actuator housing so that the microwave antenna arrangement is not affected by the pressure wave or any other mechanical influences. There is accordingly a mechanical uncoupling between the housing and the microwave antenna arrangement. 
     The guard cover means preferably includes a plastic, which has a low temperature-dependent change in volume. Suitable materials in this respect have turned out to be for example polycarbonate materials, e.g. Lexan, Makrolon or the like, or liquid crystal copolyesters or polymers (LCP), e.g. Vectra, which exhibits good strength properties and low thermal expansion. 
     The guard cover means is not electrically conductive and constitutes a dielectric so that the propagation of the microwaves, which for example are at a frequency of 10 MHz to 25 GHz, is not impaired. A particularly convenient form of the invention may even involve the guard cover means forming a sort of secondary radiant system, the dielectric constant and/or the geometry of the guard cover means being matched to suit the microwave antenna arrangement and/or the geometry of the actuator housing so that the microwaves are propagated in a predetermined mode or in predetermined modes in the motion space. 
     Preferably the guard cover means is connected in a pressure-tight manner with at least one wall of the housing in order to shield the microwave antenna arrangement in a pressure-tight fashion. This pressure-tightness is for example produced by adhesive bonding, screwing, welding or the like. In the case of the wall it may be a question of a side wall, a peripheral wall or an end wall. The guard cover means preferably engages a side wall of the housing. In the case of this side wall it can be a question of a peripheral wall of the motion space and/or of the cover, an end wall of the cover or the like. Between the respective side wall of the housing and the guard cover means preferably at least one seal is placed. If the guard cover means is injection molded on the housing or adhesively joined thereto, such a seal is admittedly advantageous but not absolutely essential. 
     The guard cover means is preferably arranged to protrude into the motion space. The guard cover means has, as part of an advantageous form of the invention, a terminal abutment for the actuator member. For instance the guard cover means can constitute a sort of impact body and/or a terminal position damper for the actuator member, for example the piston of a pneumatic cylinder. 
     The guard cover means advantageously constitutes a component of a fluid drive, and in particular of a pneumatic fluid power cylinder. It will be clear that the guard cover means is in principle also able to be employed for electric drives. The actuator member is constituted by a piston or, respectively, the rotor of the respective drive. An other design in accordance with the invention may provide for the guard cover means to be a component of a fluid valve, for example a pneumatic one. The actuator member is preferably provided for driving the valve member. For instance, the actuator member may constitute a component of the valve member. 
     In the case of the last mentioned designs the guard cover means of the invention will preferably possess at least one fluid duct connected with the motion space. 
     This fluid duct serves for example for the connection of the motion space or, respectively, of the piston chamber with a fluid connection, for example a compressed air connection. The fluid duct of the guard cover means is preferably provided with a corresponding recess, for example a blind duct and/or a projection. Such compensation means ensure that the microwaves may be propagated in the motion space in a substantially symmetrical manner. 
     The guard cover means namely preferably exhibits at least one abutment section constituting a terminal abutment for the actuator member. The fluid cable is for example provided in the abutment section. The terminal abutment projects proud of a cover section of the guard cover means for the protection of the microwave antenna arrangement in the direction of the motion space so that the actuator member impinges against the abutment section but not however against the cover section. The abutment section passes mechanical energy past the side of the microwave antenna arrangement and bears against a rear wall and/or a side wall of the housing. The abutment section is for example annular and surrounds the microwave antenna arrangement in an annular fashion. Evidently a sort of support or strut could be provided extending away from the rear wall of the housing toward the motion space and forming a terminal abutment for the actuator member. 
     The microwave antenna arrangement is preferably connected with a rear wall of the actuator housing, which for example is formed by a cover of the actuator housing. Preferably the guard cover means is also connected with this cover. For such attachment a method involving injection molding in place, adhesive bonding or screwing may be employed. All in all it is convenient for the cover to be set in place as a sort of cover module, with a guard cover means attached to it, on the actuator housing where it is fixed, for example with the aid of bolts, staples, adhesive bonding, welding or the like. 
     The actuator housing, for instance a cover of the actuator housing, preferably constitutes a component of the microwave antenna arrangement. To take an example, the microwave antenna arrangement may comprise a coupling probe, which together with the housing, forms an electrical conductive structure. The inventive guard cover means protects the sensitive coupling probe against mechanical effects. 
     The guard cover means is preferably an injection molding. The guard cover means can be manufactured separately from the actuator housing and be later for example screwed and/or adhesively bonded and/or snapped in place. It is in particular preferred however for the guard cover means to be attached by injection molding to the actuator housing, for instance a housing cover. 
     Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of embodiments thereof in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of an actuator device having a position detecting device in accordance with the invention, generally on the line A-A of  FIG. 2 . 
         FIG. 2  is a rear view of a cover of the actuator device in accordance with  FIG. 1 . 
         FIG. 3   a  is a perspective exploded view of the cover of the actuator device in accordance with  FIG. 2  with a guard cover means, an antenna body and a holding body for holding the antenna pole body with a clearance at or a distance from the cover. 
         FIG. 3   b  shows the cover with the components according to  FIG. 3   a  in the fitted condition. 
         FIG. 4  is a perspective view of the antenna pole body according to  FIG. 3   a.    
         FIG. 5  is a partially diagrammatic view of the position detecting device of the actuator device as shown in  FIG. 1 . 
         FIG. 6  is a cross sectional view generally as shown in  FIG. 5  of a further actuator device with a second embodiment of a guard cover means in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fluid power device is in the form of an actuator device  11  and in particular a pneumatic fluid power cylinder  10 . A piston  13  runs in a housing  12  and constitutes an actuator member  14  reciprocating in a linear manner. By way of fluid or compressed air connections  15  and  16  compressed air  17  may flow into a chamber  18 , which constitutes a motion space  19  for the actuator member  14 , and leave it again for driving the piston  13 . 
     A middle part  20  of the housing  12 , for example of metal, is tubular in configuration and has an inner cross section matching an outer cross section and is for example essentially circular. A bearing cover  23  and a terminal cover  24  on the front and rear ends  21  and  22  of the housing  12  close the chamber  18  in a pressure-tight manner. For instance, between the a side wall or peripheral wall  25  of the middle part  20 , which delimits the chamber  18  to the outside, and the more particularly metallic covers  23  and  24  seals  26  and  27  are disposed for example, in the form of O-rings. The covers  23  and  24  are screwed in place by bolts  28  on the middle part  20 . The bolts  28  for example screwed into bead-like reinforcing and holding ribs  29 , which extend along the outer periphery of the housing  12  in the longitudinal direction  30  of the drive cylinder and are disposed in the corner portions of the housing  12 , which for example has an essentially rectangular outline. The holding ribs  29  have holes  74 , for example in the terminal cover  24 , which the bolts  28  extend right through. 
     The piston  13  is screwed by means of screw arrangement  31  on a piston rod  32 . Instead of a screw arrangement  31  a terminal damping means could be placed on the piston  13 . Around the piston  13  there extends in an annular manner a seal  33 , which divides up the chamber  18  into two space parts in a sealing fashion from each other. The piston rod  32  constitutes a power or force transmitting member, which extends through the bearing cover  23 . At the free end of the piston rod  32  attachment means  34 , for example an annular flange, are arranged for securing the objects to be actuated. The piston rod  32  runs in a bearing  35  in the bearing cover  23  or end plate. A seal  36 , through which the piston rod  32  extends, of the bearing cover  23  constitutes a pressure-tight termination of the chamber  18 . 
     With the aid of assembly means, which for example include an assembly hole in the bearing cover  23 , the actuator device  11  is able to be secured on a holding means. 
     The piston  13  is able to run longitudinally between the bearing cover  23  and the terminal cover  29  in the longitudinal direction of extent as indicate by the arrow  30 ′. A position detecting device  40  detects the clearance  41  of the actuator member  14  from its terminal position  42  in the vicinity of the terminal cover  24 . The position detecting device  40  operates on the basis of microwaves, for example in a range of 1 MHz and approximately 25 GHz or more particularly 3 GHz and 10 GHz, which are emitted by a microwave antenna arrangement  43  with a coupling probe  44  into the motion space  19 , which on its inner face at least is essentially electrically conductive and accordingly constitutes a conductive structure  45  for the microwaves. 
     The actuator member  14  forms a specimen  46  which reflects the microwaves. In a manner dependent on the respective position of the specimen  46  in the motion space  19 —one position of the actuator member  14  remote from the terminal end  42  is indicated in chained lines—the phase of the microwaves emitted and received by the microwave antenna arrangement  43  will vary. On the basis of the phase relationship and/or the transit time of the microwaves it is possible for an evaluating means  47  of the position detecting device  40  to detect the position of the actuator member  14  in the motion space  19  and for example to signalize same to a control device, not illustrated, for the control of the actuator device  11 , for example a memory programmed control device. The evaluating means  47  for example comprises an emitting means and a receiving means for the emission and reception of the microwaves by means of the coupling probe  44  and other components  80 , for example a digital signal processor, a bus coupler, an emission and/or reception means for wired or wireless emission and reception of position signals by means of an antenna  38  to the master control and the like. 
     The evaluating means  47  includes for example a high frequency board  48  with components (not described in detail) and conductive tracks for producing microwaves and furthermore an evaluating board  49  which for example includes a bus coupler. The boards  48  and  49  are connected together electrically, for example using a plug cable  50 . A cover  51  shields the boards  48  and  49 , which are disposed for instance in chamber  55  in the housing  12  or, respectively, the terminal cover  24 , against environmental influences. 
     The microwave antenna arrangement  43  comprises an electrically insulating or dielectric holding body  52 , which for example has a stepped cylindrical configuration and for example is manufactured of an electrically insulating plastic, in particular one with a low coefficient of thermal expansion. The holding body  52  holds an at least externally electrically conductive antenna pole body  54  of the microwave antenna arrangement  43  in a central position and more particularly coaxially. The holding body  52  and hence the microwave antenna arrangement  43  are held centrally and in particular coaxially in relation to the measurement and, respectively, motion space  19  on a rear end wall  53  of the terminal cover  24 , as for example by being plugged, inserted and adhesively bonded, screwed or held in some other fashion on the terminal wall  53  in a corresponding recess or socket  85 . 
     First pole faces of the antenna pole body  54  cooperate with second pole faces of the housing  12  of the conductive structure  45 . The antenna pole body  54  extends right through the holding body  52  and is connected by a conductor  84  electrically with the high frequency board  48 . The electrically conductive terminal wall  53  and accordingly the housing  12  are connected by way of, for example, a flexible conductor  56  with the high frequency board  48 . 
     A front umbrella-like terminal end wall  76  of the antenna pole body  54 , which is disposed to the fore on a central cylindrical antenna part  77 , which may have an annular groove  86  for example, extends past the measurement and motion space  19  and is connected by means of a electrical conductor section  78  with the high frequency board  48 . The conductor section  78  is trained through the holding body  52  and a channel  87  in the terminal wall  53 , preferably at an insulating clearance from the terminal wall  53 , to the high frequency board  48  and connected directly, or by way of the preferably flexible conductor  84 , with a mechanical decoupling effect, with the high frequency board  48 . The terminal  78  lies on a terminal or end side  88  of a front part  81  of the holding body  52 , and more particularly on projections  79  with a circularly segment-like form. The front part  81  has a larger periphery than a rear section  82  of the holding body  52 , which is taken up in the socket  85 . The front part  81  rests on the terminal wall  53  to the front or, respectively, projects past the terminal wall  53 . 
     The microwaves pass in a direction away from the motion space  19  and change from a coaxial mode into a wave guide mode. 
     The antenna pole body  54  is for example an essentially metallic insert member, which is adhesively bonded and/or welded to the holding body  52  and more particularly i adhesively bonded or welded in the receiving space  59 . In accordance with a modification of the invention the antenna pole body  54  is joined to the holding body  52  in a casting method or more especially an injection casting method. 
     The position of the microwave antenna arrangement  43  in relation to the housing  12  or, respectively, the motion space  19 , and however in particular the position of the antenna pole body  54  in relation to the conductive structure  45 , which cooperates with the microwave antenna arrangement  43 , is essential for exact determination of the clearance or distance  41 . In order for such clearances to the adhered to and a high accuracy of measurement to be obtained in the case of the actuator device  11  the following measures are taken. 
     A guard cover means  60  is disposed in front of the microwave antenna arrangement and protects the microwave antenna arrangement  43  against mechanical effects due to the actuator member  14 . The guard cover means  60  comprises an annular abutment section  61 , which projects to the front of a cover-like section  62  toward the motion space  19  and constitutes an abutment  63  for the actuator member  14 . For instance an annular projection  37  on the piston  13  strikes against the abutment  63 . The projection  37  may be a hard or elastic, resilient ring. The abutment section  61  constitutes a sort of ring, which extends around the microwave antenna arrangement  43  and bears against the rear wall or end wall  53  of the terminal cover  24 . Accordingly any mechanical forces caused by impact of the actuator member  14  on the abutment  63  are passed on to the terminal cover  24  and accordingly the housing  12  and prevented from affecting the microwave antenna arrangement  43 . 
     The cover section  62  constitutes a sort of floor or intermediate platform in the abutment ring  64 , which in the present case is made integral with the abutment section  61 . A multi-part design with for example screwed together and/or adhesively bonded components for an inventive guard cover means is also possible. 
     The guard cover means  60  seals the microwave antenna arrangement  43  off from the pressure space and, respectively, the motion space  19  in a pressure-tight fashion. To take one example, the cover section  62  may be integral with the abutment ring  64  so that between the two part no pressure blast may move toward the microwave antenna arrangement  43 . Furthermore, on the outer side of the abutment ring  64  seals  65  and  66 , e.g. o-ring seals are placed between outer periphery of the abutment ring  64  and the peripheral wall  25  of the middle part  20  and a peripheral wall  67  of the terminal cover  24 . The guard cover means  60  has for example sockets  65 ′ and  66 ′, as for example peripheral grooves, to accept the seals  65  and  66 . 
     The abutment ring  64  projects past the terminal cover  24  and extends into the middle part  20 . At its front section, between the abutment  63  and the intermediate platform, which constitutes the cover section  62 , the abutment ring  64  defines a receiving space  68  for the screw arrangement  31  or a terminal position damping means, not illustrated. 
     Between the guard cover means  60  and the microwave antenna arrangement there is a clearance or distance  69 , into which the cover section  62  may deform, for example owing to a pressure wave or blast, which is caused by the actuator member  14 . Accordingly the guard cover means  60  and the microwave antenna arrangement  43  are decoupled from each other mechanically and the microwave antenna arrangement  43  is protected against pressure loads. 
     The guard cover means  60  comprises a fluid duct  70  for connection of the chamber  18  with the compressed air connection  16 , which for example extends through the abutment ring  64 . 
     In order for the microwaves to propagate in the motion space  19  in a substantially symmetrical manner, the fluid duct  70  is provided with a blind duct  71  as a compensating means  71 , such duct running along the side of the abutment ring opposite to the fluid duct  70 . The blind duct  72  terminates at the peripheral wall  67  i.e. the peripheral wall  67  closes the blind duct  72  in the radially outward direction. The compensating means  71  can also exhibit a projection  73  instead of the blind duct  72  as an example. The projection  73  is for example a ring, a ring segment, a cone or the like. 
     The guard cover means  60  comprises a dielectric material and in particular a plastic with a low coefficient of thermal volumetric expansion, for example Lexan, Vectra or the like. The guard cover means  60  is matched to suit the radiant characteristic of the microwave antenna arrangement  43  so that the microwaves, which are emitted by the microwave antenna arrangement  43 , are propagated in a predetermined mode in the conductive structure  45  or, respectively, the motion space  19 . 
     The guard cover means  60  is preferably, as illustrated in  FIG. 3   b  for example, premounted as a whole on the terminal cover  24 , and for example plugged in place, adhesively bonded in place, held by detent means and/or screwed in place. Accordingly the guard cover means  24  may be attached bodily in position with the guard cover means  60  already fitted. The guard cover means  60  furthermore constitutes a sort of cover to prevent pressure waves finding their way by way of the microwave antenna arrangement to the evaluating means  47 , which is disposed and protected on the rear side of the rear wall or end wall  53  of the terminal cover  24 . 
     A front part  90  of the guard cover means  60  has a larger diameter than rear part  91  so that between the front and the rear part  90  and  91  an abutment  92 , as for example a projection, is formed. When the guard cover means  60  is plugged into a socket  93  in the terminal cover  24 , the abutment  92  rests on an end face  94  of the peripheral wall  67  of the terminal cover  24 . Accordingly the guard cover means  60  bears not only on the rear end wall  53  of the terminal cover  24 , which constitutes the floor of the socket  93 , but also on the end face  94 . 
     The front part  81  standing proud of the end wall  53  of the holding body  52  is surrounded in a pressure-tight manner by the guard cover means  60  in order to avoid mechanical loads due to the actuator member  14  as it moves close to the microwave antenna arrangement  43 . The front part  81  or, respectively, the end wall  76  of the antenna body  54  is arranged in a chamber  57  of the guard cover means  60  at the clearance  69 . The chamber  67  is formed by the floor-like cover section  62  and a rear side wall  58 , which is a component of the abutment section  61 . 
     A pneumatic power cylinder  10 ′ i.e. an actuator means  11  as shown in  FIG. 6  is essentially similar to the power cylinder  10 . To this extent in  FIG. 6  identical or similar components are denoted by the same reference numerals or reference numerals partly an apostrophe ′ to distinguish them. 
     Unlike the guard cover means  60  the guard cover means now projects less to the fore toward the measuring and motion space  19 ′. It does not have fluid ducts so that no compensation means are necessary either. The guard cover means  60 ′ bears completely on an end wall  53 ′ of a terminal cover  24 ′. An abutment ring  64 ′, which constitutes an abutment section  61 ′, projects to the fore in the direction of the motion space  19 ′ and forms an abutment  63 ′ for the piston  14 ′. A cover section  62 ′ is set back behind the abutment  63 ′ and has an edge part  95  in engagement with the end wall  53 ′. 
     A socket  85 ′ of the terminal cover  24 ′ for the microwave antenna arrangement  43  is lower down than the end wall  53 ′ so that the microwave antenna arrangement  43  is set back in relation to the end wall  53 ′ and is at a clearance  69 ′ from the guard cover floor or, respectively, cover section  62 ′. Into the clearance  69 ′ the cover section  62 ′ may deform, for example owing to a pressure wave caused by the actuator member  14 ′. The coupling board  49 ′ is connected in a wired manner by way of a conductor  96  with a control device, not illustrated, for the fluid power cylinder  10 ′, which sends the position detect signals relative to the position of the actuator member  14 ′ in the motion space  19 ′. 
     The clearance  69 ′ or clearance can be at least partially filled with a yielding and more particularly elastic material.