Actuator with Position Sensing Device

Abstract

The invention relates to an actuator, in particular pneumatic cylinder, with an actuator element movably located in a movement space of a housing and with a microwave position sensing device for detecting the position of the actuator element in the movement space, with a microwave aerial arrangement for the transmission of microwaves into the movement space forming a waveguide and for the reception of reflection microwaves generated by the reflection of the transmitted microwaves at the actuator element from the movement space, and with evaluation means for the generation of a position signal representing the current position of the actuator element from the reflection microwaves. In the actuator, it is provided that the actuator element has a groove arrangement with at least one groove for reflecting the microwaves.

Description

The invention relates to an actuator, in particular a pneumatic cylinder, with an actuator element movably located in a movement space of a housing and with a microwave position sensing device for detecting the position of the actuator element in the movement space, with a microwave aerial arrangement for the transmission of microwaves into the movement space forming a waveguide and for the reception of reflection microwaves generated by the reflection of the transmitted microwaves at the actuator element from the movement space, and with evaluation means for the generation of a position signal representing the current position of the actuator element from the reflection microwaves.

An actuator of this type is for example known from DE 198 33 220 A1 or from DE 10 2006 206.1, which is not subject to prior publication.

The actuator may for example be a pneumatic cylinder the piston of which forms an actuator element installed for linear movement into a piston chamber of the housing. The piston chamber or movement space is electrically conductive on the inside, for example owing to a metal housing, so that the movement space forms a waveguide. The microwaves spread from the aerial arrangement towards the piston and are reflected by the piston. The evaluation means detect the position of the piston, for example using the reflection time between the outgoing microwave and the returning reflection microwave.

The outer circumference of the piston is usually fitted with a seal made of a dielectric material. As a result, the piston does not represent an ideal waveguide short-circuit. There are further actuator elements or pistons made of plastic, which do not reflect the microwaves. The microwaves or waveguide waves then partially pass the actuator element or piston and are only reflected by an end face of the movement space placed opposite the aerial arrangement. As a result, the microwaves are entirely or partially reflected not by the actuator element as desired, but rather by an opposite end wall of the housing, so that the position of the actuator element can only be detected with difficulty if at all.

The present invention is therefore based on the problem of improving measuring accuracy in the detection of the position of the actuator element.

To solve this problem, it is provided in an actuator of the type referred to above that the actuator element has a groove arrangement with at least one groove for reflecting the microwaves.

The microwaves transmitted by the aerial arrangement are reflected with the aid of the groove arrangement. Even a single groove improves the reflection characteristics of the actuator element. Expediently two, three or more grooves are provided.

The microwave aerial arrangement may for example transmit microwaves in the so-called E01 mode or in the H11 mode in the circular waveguide. If the transmitted E01 microwaves meet a coaxial obstruction, such as a piston, they are partially reflected or partially converted into a coaxial TEM wave. In this short section of coaxial conductor, the piston represents the inner conductor, the seal between the piston and the cylinder wall the dielectric and the cylinder wall the outer conductor. If an H11 wave meets a coaxial obstruction, a field pattern corresponding to a higher mode in a coaxial line, i.e. an H11 wave in a coaxial line, is created.

The movement space expediently forms an outer conductor of a coaxial line for the microwaves, where the microwaves spread in the E01 or the H11 mode. The groove arrangement may for example be provided on an inner conductor section of the coaxial line. In this case, the groove arrangement impedes the current flow at the inner conductor section. Only a part of the current, if any, can flow across the groove. This results in a local reflection of the electromagnetic wave and thus in an at least additional desirable reflection of the total wave impinging on the actuator element.

The groove arrangement may be provided at different points of the actuator element. The groove arrangement is expediently located on an outer circumference of the actuator element. In this case, the groove arrangement may extend either over the entire outer circumference or over segments of the circumference of the actuator element. If the groove arrangement extends over segments of the circumference, the actuator element is advantageously secured against rotation in the movement space.

The at least one groove or the groove arrangement could however conceivably be provided on a recess or a projection of the actuator element. An actuator element may obviously comprise several groove arrangements, for example on an outer circumference, a projection or the like. The grooves on the projection or recess may extend over a part or segment of the circumference or over the entire outer circumference of the projection or the entire inner circumference of the recess.

By means of the groove arrangement, the movable actuator element reflects the microwaves, which may for example be coupled into the movement space with the aid of a coupling probe of the microwave aerial arrangement. Using a reflection time measurement and/or a phase comparison between transmitted and received microwaves, which may have a frequency range of 10 MHz to 25 GHz—preferably 1 GHz to 25 GHz—the position sensing device detects a position of the actuator element in the movement space. The position sensing device may for example measure the distance of the actuator element from an end stop in the region of the microwave aerial arrangement.

The actuator, which may be an electric or fluid-powered drive, has a housing with an electrically conductive movement space in which an actuator element, for example a rotor of an electric motor or a piston of a pneumatic drive, is movably installed. The actuator expediently is a linear actuator. In this case, the actuator element is capable of linear movement. The principle of the invention can, however, also be applied to a rotary or semi-rotary actuator.

The actuator may be driven electrically and/or by fluid power, for example pneumatically or hydraulically. A so-called hybrid drive with both electric and fluid power operation is also advantageous.

In a further variant of the invention, it may be provided that the position sensing device is a part of a fluid valve, for example a pneumatic valve. In this case, the actuator element is the valve member of the fluid valve, for example a drive piston by which the valve member is driven pneumatically.

The groove may for example have a rectangular internal contour. The base region may for example have a rectangular shape. Polygonal, V-shaped, U-shaped or circular internal contours are obviously conceivable as well.

The recess or projection with the groove arrangement may form a part of a cushion arrangement for the reduction of the end-of-stroke speed of the actuator element in the region of an end stop of the housing or the movement space. The groove arrangement for example comprises a recess or is located on a recess into which a projection on the housing can dip. This projection may for example be a part of a cushion arrangement. As the actuator element approaches the end stop, the projection on the housing engages the recess in the actuator element, or the projection on the actuator element engages the recess of the housing and blocks a fluid passage provided for the entry and discharge of fluid. Now the fluid, for example compressed air, can only flow out in a restricted manner through an outlet passage, thus reducing the end-of-stroke speed of the actuator element in the region of the end stop.

The recess or the projection with the groove arrangement according to the invention and the microwave aerial arrangement are expediently coaxial.

The at least one groove may be hollow or filled with a dielectric material. The groove arrangement may comprise both hollow grooves and grooves filled with a dielectric material. A groove may further conceivably be partly hollow and partly filled with a dielectric material. The dielectric material, for example plastic, rubber or the like, may be applied to the actuator element by injection moulding. Alternatively, the dielectric material may be a separate component fitted to the actuator element in an assembly process.

The depth of the at least one groove is expediently approximately ¼ of the wavelength of the microwaves spreading in the region of the interior of the at least one groove. The interior may for example be hollow, so that the microwaves have a wavelength corresponding to propagation in air. As explained above, however, the interior may be wholly or partially filled with a dielectric material. In this case, the depth of the at least one groove is expediently determined by the dielectric constant of the material. The depth of the groove is expediently less than ¼ of the wavelengths of the microwaves with reference to air as propagation medium. The wavelength of the microwaves in air may for example be λ0; the wavelength λ of the microwaves in the region of the dielectric in the at least one groove is calculated as follows.

$\begin{array}{cc}\lambda =\frac{\lambda 0}{\sqrt{\varepsilon r}}& \left(1\right)\end{array}$

wherein ∈r is the dielectric constant of the dielectric material. The depth of the grooves may for example be 2 mm to 5 mm.

The spacing of the grooves of the groove arrangement is expediently less than the depth of the grooves themselves. It may for example be significantly less than ¼ of the wavelength of the microwaves. As explained above, the wavelength of the microwaves is determined by the dielectric used, for example air or plastic. The spacing and the depth of the grooves are matched to the operating frequency of the microwaves.

In one variant of the invention, the grooves of the groove arrangement may be provided on the actuator element exclusively for reflection purposes. Alternatively, the groove arrangement may conceivably act as or include a holder for at least one further component of the actuator element. One or more grooves may for example be provided to form a seal arrangement or a device for guiding the actuator element. The grooves may further conceivably include separate retaining grooves for the retention of the further component, for example the seal arrangement. The further component, for example a sealing ring or the like, may alternatively engage only a part-section of the groove of the groove arrangement.

The actuator element may comprise a plastic actuator body on which the groove arrangement is located. The groove arrangement may for example be provided on an electrically conductive component on the plastic actuator body. This component may for example be a sleeve installed into a location of the plastic actuator body or projecting from the plastic actuator body.

The groove arrangement may further include an electrically conductive coating on the actuator element. The actuator element may for example be provided with grooves, for example produced by milling, which are given an electrically conductive coating. It is further conceivable that a plastic component with the groove arrangement is fitted to the actuator element, the grooves of the plastic component being provided with the conductive coating.

Embodiments of the invention are explained below with reference to the drawing. Of the drawing:

FIG. 1 is a cross-sectional view of a pneumatic cylinder with a piston having grooves arranged on its outer circumference;

FIG. 2 is a cross-sectional view of a pneumatic cylinder with a cushioning projection having grooves arranged on its outer circumference provided on a piston;

FIG. 2b shows a piston which can be installed into the cylinder according to FIG. 2 as an alternative;

FIG. 3a is a diagrammatic cross-sectional view along line A-A of the cylinder from FIG. 2 with microwaves in the E01 mode;

FIG. 3b is a diagrammatic cross-sectional view along line B-B of the cylinder from FIG. 2 with microwaves in the TEM mode;

FIG. 4 is a cross-sectional view of a rodless operating cylinder with a recess where the grooves are provided;

FIG. 5a is a cross-sectional view of the operating cylinder according to FIG. 4 along line C-C with microwaves in the H11 mode;

FIG. 5b is a cross-sectional view of the cylinder according to FIG. 4 along line D-D with H11 microwaves as the higher mode in a coaxial line;

FIG. 6a is a cross-sectional view of a piston of a pneumatic operating cylinder according to prior art;

FIG. 6b is a cross-sectional view of a piston resembling the construction shown in FIG. 6a, but provided with grooves according to the invention;

FIG. 7 is a cross-sectional view of a piston with hollow grooves on its outer circumference; and

FIG. 8 shows a piston of an operating cylinder with grooves partially filled with a dielectric material.

Similar components of the embodiments described below or components of similar action are identified by the same reference numbers and described only once.

A pneumatic operating cylinder 11a forms an actuator 10a, in particular a fluid-power actuator. In a movement space 12 of an actuator housing 13a, an actuator element 14a capable of linear reciprocating movement is located. The actuator element 14a is represented by a piston 15a of the operating cylinder 11. The illustrated embodiment is a pneumatic operating cylinder with a piston rod, but rodless variants, electric drives or combined electro-pneumatic drives, in particular linear drives, are possible alternatives.

A valve assembly 16, for example comprising a 2/2-way valve, feeds compressed air 17 from a compressed air source 18 through pneumatic ports 19, 20 into the movement space 12 or allows compressed air to be discharged from the pneumatic ports 19, 20 to drive the piston 15a, which divides the movement space 12 into two part-chambers not identified in detail. For this purpose, a seal 21a is for example provided on the outer circumference of the piston 15a.

An end face of a central part 22 of the housing 13 is sealed by a bearing cap 23a and a cover 24a, thus bounding the movement space or piston chamber 12. A piston rod 25 forming a power take-off element of the operating cylinder 11a passes through the bearing cap 23a at an opening 26 provided with a seal.

A position sensing device 50 is provided to detect the position of the actuator element 14a within the movement space 12, for example a distance 28 of the piston 15a from an end stop 27 on the cover 24a.

The microwave aerial arrangement 51 for example comprises a coupling probe for transmitting and receiving microwaves at a high frequency, for example in a frequency range of approximately 10 MHz to 25 GHz. The coupling probe may be a metallic probe or a plastic element with electrically conductive surfaces.

The microwave aerial arrangement 54 is connected to a high-frequency device 52, for example a high-frequency circuit board or the like, and to an evaluation device 53.

With the aid of the high-frequency device 52, microwaves 54 can be generated to be coupled into the movement space 12 by the microwave aerial arrangement 54. The movement space 12 forms a waveguide 56 which guides the microwaves 54 to the actuator element 14a, which reflects the microwaves 54 and generates reflection microwaves 55.

The microwave aerial arrangement 51 may be located in a dielectric section of the cover 24a. Apart from that, the cover 24a is expediently made of metal. The central part 22 and the cap 23a are expediently also made of metal. In any case, an inner wall 29 of the central part 22 is electrically conductive to form the waveguide 56.

The high-frequency device 52 comprises input elements and output elements not identified in detail, such as capacitors, millimetre wave integrated circuits (MMICs), directional couplers or the like. The high-frequency device 52 is advantageously able to transmit the microwaves 54 in different frequencies and in further frequencies not identified in detail, for example with the aid of a voltage-controlled oscillator (VCO) or the like.

The high-frequency device 52 and the evaluation device 53, which comprises or represents evaluation means according to the invention, are electrically connected to one another and may be fitted to a common support structure. The high-frequency device 52 and/or the evaluation device 53 may be located in or on the cover 24a.

Using the reflection time of pulses of the microwaves 54, 55 (pulse radar), the phase shift between outgoing microwaves (54; 54′) and returning microwaves (55) (interferometer method), an FMCW (frequency modulated continuous wave) process or the like, the evaluation device 53 determines the position, which may for example correspond to the distance 28 of the actuator element 14a within the movement space 12. The evaluation device 54 and/or the high-frequency device 52 may for example comprise a mixing device for mixing, for example multiplying, the transmitted microwaves 54 and the reflected microwaves 55, a processor, a memory and/or further electronic components, such as ASICs (application specific integrated circuits) or the like. The evaluation device 53 transmits a position signal 57 representing the current position of the actuator element 14a to a superior control unit S by wireless means, for example using an aerial 58, or via a line 59.

On an outer circumference 30 of an actuator body 31a, for example a metal body or an electrically conductive, for example coated, plastic body, a groove arrangement 32a with grooves 33a is provided.

The electrically non-conductive seal 21a would allow a partial penetration of the microwaves 54 into the space behind the piston, which would be undesirable. The groove arrangement 32a, however, reflects virtually all of the microwaves 54, so that the reflection microwaves 55 are generated.

The depth 34a of the grooves 33, which may have a rectangular cross-section, is matched to the frequency or wavelength of the microwaves 54. This takes account of the dielectric quality of the seal 31a extending into interior spaces 35 of the grooves 33a. The depth 34a may for example be ¼ of the wavelength of the microwaves 54 in the region of the interior spaces 35, the wavelength of the microwaves being reduced in the region of the interior spaces 35 in dependence on the relative permittivity of the material for the seal 21a.

A pneumatic operating cylinder 11b includes some components which are identical with or similar to those of the operating cylinder 11a.

On a cover 24b, a cushion arrangement 36b is provided to cushion the impact of a piston 15b representing an actuator element 14b on an end stop 27 in the region of the cover 24b. As the piston 15b approaches the end stop 27, a cushioning projection 37 projecting in front of the piston 15b dips into a recess 38 in the region of the cover 24b or on a cushioning ring 38′ placed in front of the cover 24b in a final movement section. Now compressed air can no longer flow out of the movement space or the piston chamber through a passage 39. Air can only be discharged from the movement space 12 through an outlet passage 40. A preferably adjustable restrictor 41 is expediently provided on the outlet passage 40. The reduced cross-section of the outlet passage 40 cushions the stroke of the piston 15b in the region of the end stop 27.

The cushioning projection 37 is provided with a groove arrangement 32b with grooves 33b. the groove arrangement 32b reflects the microwaves 54 to generate the reflection microwaves 55.

The grooves 33b are formed on a groove component 42 located on a projection body 43 of the cushioning projection 37. The groove component 42 may for example be sleeve-like. The grooves 33b are provided on an outer circumference of the groove component 42. The projection body 43 may for example be made of plastic or of another dielectric material. The groove component 42 is electrically conductive at least in the region of the groove arrangement 32b, for example being provided with an electrically conductive coating or because the groove component 42 is made of metal.

The grooves 33b may alternatively be provided on an outer circumference of a projection body 43′ of a piston 15b′, which can replace the piston 15b. The projection body 43′ may be made of metal. The grooves 33b are for example milled in.

The interior spaces 35 of the grooves 33b may be filled with a dielectric material 47. In this case, the depth 34b of the grooves 33b would be less than if they were “only” filled with air.

The microwaves 54, 55 spread in the region between the end stop 27 and the cushioning projection 37 in the E01 mode (FIG. 3a) while changing at least partially to the TEM mode (FIG. 3b) in the region of the cushioning projection 37.

An actuator 11c is represented by a pneumatic operating cylinder. The operating cylinder 11b is a so-called rodless operating cylinder, i.e. no piston rod is fitted to the actuator element 14c represented by a piston 15c. The piston 15c is capable of linear reciprocating movement in the movement space 12 between the covers 23c, 24c. Cushion arrangements 36c, 36c′ are provided on the covers 23c, 24c. Passages 39 lead from the pneumatic ports 19, 20 to cushioning projections 37c on the covers 23c, 24c. The compressed air flows through the passages 39 into the movement space 12 or is discharged therefrom to drive the piston 15c.

As the piston 15c approaches the end stops 27 adjacent to the projections 37c, the projections 37c dip into recesses 38c, 38c′ in the piston 15c in a last movement section before reaching the end stops 27. This blocks the passages 39, allowing no further air to flow into the inlet or outlet port of the discharge-side passage 39 on the projection 37c. The air now flows out of the movement space 12 through outlet passages 40 terminating in the passages 39. The passages 40 are preferably fitted with adjustable restrictors 41.

A position sensing device 50′ generates microwaves 54′ in the so-called H11 mode with an aerial arrangement 51′. The aerial arrangement 51′ is provided on the cover 24c, preferably in a dielectric region. FIG. 5a shows the microwaves 54′ in a section between the end stop 27 and the piston 15c. In the region of the recess 38c, the microwaves 54′ become so-called H11 waves as a higher mode in a coaxial line.

A groove arrangement 32c with grooves 33c is provided in the recess 38c′. The grooves 33c reflect the microwaves 54′.

The grooves 33c are provided on an outer circumference of a metallic sleeve 44. The sleeve 44 contains the recess 38c′ for the cushioning projection 37c. In principle, grooves 33c on the outer circumference of the sleeve 44 would be sufficient. The sleeve 44 may for example be made of metal. In the present case, a base 45 of the sleeve 44 is made of metal as well. The electrically conductive base region 45 is however not required.

The piston 15c comprises an actuator body 31c on which the sleeve 44 with the groove arrangement 32c is located. The sleeve 44 may for example be installed into a recess 46 on the actuator body 31c, which may be made of plastic or metal.

There are no grooves on the recess 38c on the side of the piston 15c which is remote from the aerial arrangement 51′.

In principle, grooves could be provided, for example by milling, on the recess 46 for the sleeve 44 rather than on the sleeve 44 itself, which is an electrically conductive component on the actuator body 31c. If the actuator body 31c is made of plastic, these grooves may for example be given an electrically conductive coating, for example using a physical or chemical vapour deposition process (physical vapour deposition/PVD; chemical vapour deposition/CVD).

There are no grooves or groove arrangements on the outer circumference of the pistons 15b, 15c. The outer circumference of the pistons 15b, 15c is fitted with seals 21b, 21c.

In place of the piston 15a, a piston 60 as shown in FIG. 6b could be used. The piston 60 has an annular piston body 61 with a location 62, for example for the piston rod 25. On the outer circumference of the piston body 61, a central slot 63 is located between slots 64. The slots 63, 64 are circumferential grooves. The central slot 63 accommodates an annular magnet 71 provided for triggering conventional position sensors such as magneto-restrictive sensors or Hall elements. The lateral annular slots 64 are grooves 65 of a groove arrangement 66 provided to reflect microwaves.

The piston body 61 is extrusion-coated with an elastic sealing material forming a seal 67. The seal 67 is made of a dielectric material and fills the grooves 65. The seal 67 comprises seal sections 68 extending radially outwards at an angle, which may for example bear tightly against the inner wall 29. Between the annular seal sections 68, a recess 69 for a guide band 70 is provided.

A piston 60′ shown in FIG. 6a is a conventional piston without any grooves 65 for reflecting microwaves. A piston body 61′ of the piston 60′ is only provided with the central slot 63 for accommodating the magnet 71.

In place of the piston 15a, a piston 75 according to FIG. 7 could be used. Grooves 76 of a groove arrangement 77 are provided on the outer circumference of the piston 75. The grooves 76 are continuous annular grooves. If the piston 75 were secured against rotation but capable of linear movement in the movement space 12, for example owing to a polygonal cross-section of the movement space 12 or owing to the provision of a guide arrangement, such as a longitudinal slot for the piston 75, the grooves 76 could conceivably extend only over a part of the circumference of the piston 75.

The grooves 76 have a rounded base region. The grooves 76 are provided on an outer circumference of an actuator body 78 which may for example be made of metal. The grooves 76 are substantially hollow.

The outer circumference of the actuator body 78 supports a seal 80, for example an O-ring, which seals the grooves 76 radially on the outside.

The depth 79 of the grooves 76 is greater than a depth 79′ of grooves 76′ of a groove arrangement 77′ on an actuator element 75′. The grooves 76′ are partially filled with a dielectric material, which may be represented by sections of a seal 80′ of the actuator element 75′ which project radially inwards.

It is understood that the invention can also be implemented in an electric drive or an electro-fluidic hybrid drive. The piston 60′ with its magnet 71 could for example be driven by a field coil arrangement 100 as shown for the actuator 10a by way of example. The field coil arrangement 100 forms an electric drive component 101 for driving the actuator element 101.

Claims

1. An actuator comprising:

a pneumatic cylinder;

an actuator element movably located in a movement space of a housing;

a microwave position sensing device for detecting the position of the actuator element in the movement space,

a microwave aerial arrangement for the transmission of microwaves into the movement space forming a waveguide and for the reception of reflection microwaves generated by the reflection of the transmitted microwaves at the actuator element from the movement space; and

evaluation means for the generation of a position signal representing the current position of the actuator element from the reflection microwaves, the actuator element having a groove arrangement with at least one groove for reflecting the microwaves.

2. The actuator according to claim 1, wherein the waveguide acts as an outer conductor of a coaxial line for the microwaves and the groove arrangement is located on an inner conductor section of the coaxial line, the groove arrangement at least partially preventing a current flow along the inner conductor section and thus acting as a reflection body.

3. The actuator according to claim 1 wherein the groove arrangement is located on an outer circumference of the actuator element.

4. The actuator according to claim 1 wherein the groove arrangement is located on a recess of the actuator element.

5. The actuator according to claim 1 wherein the groove arrangement is located on a projection of the actuator element.

6. The actuator according to claim 5, wherein a recess of the actuator element or the projection forms a part of a cushion arrangement for reducing the end speed of the actuator element in the region of an end stop of the housing.

7. The actuator according to claim 1 wherein the groove arrangement has a recess or is located on a recess into which a projection on the housing can dip.

8. The actuator according to claim 3 wherein the groove arrangement is provided on the entire outer circumference or at least on a segment of the circumference of the actuator element or of the projection of the actuator element or on the entire inner circumference or at least on a segment of the inner circumference of a recess of the actuator element.

9. The actuator according to claim 1 wherein the groove arrangement and the microwave aerial arrangement are coaxial.

10. The actuator according to claim 1 wherein the at least one groove has a rectangular internal contour.

11. The actuator according to claim 1 wherein the at least one groove is hollow or filled with a dielectric material.

12. The actuator according to claim 1 wherein the at least one groove has a depth corresponding to approximately a quarter of the wavelength of the microwaves spreading in the region of the interior space of the at least one groove.

13. The actuator according to claim 12, wherein the interior space is filled with a dielectric material and the depth of the at least one groove is less than a quarter of the wavelength of the microwaves with reference to air as propagation medium.

14. The actuator according to claim 1 wherein the spacing of the grooves of the groove arrangement is less than the depth of the respective grooves.

15. The actuator according to claim 1 wherein the groove arrangement forms or includes a holder for at least one further component of the actuator element, in particular for a seal arrangement and/or for a guide device for guiding the actuator element in the movement space.

16. The actuator according to claim 1 the actuator element comprises an actuator body, in particular a plastic actuator body, on which the groove arrangement is located.

17. The actuator according to claim 1 the groove arrangement is located on an electrically conductive groove component provided on the actuator body.

18. The actuator according to claim 1 wherein the groove arrangement includes an electrically conductive coating provided on the actuator element.

19. The actuator according to claim 1 wherein the actuator it is a rodless pneumatic operating cylinder or a pneumatic operating cylinder with a piston rod.

20. The actuator according to claim 1 wherein the actuator comprises an electric drive or an electric drive component.