DE102020130625A1 - Clamping device with shape memory alloy, sensor with such a clamping device and method for clamping a component - Google Patents

Abstract

The present invention describes a clamping device for clamping and holding a component, with at least one movable clamping element for contact with the component, wherein the clamping element can be moved between a clamping position and a loose position by means of a drive device, characterized in that the drive device is a drive element made of a shape memory material includes.

Description

The invention relates to a clamping device for clamping and holding a component according to the preamble of patent claim 1. The invention also relates to a sensor with such a clamping device according to patent claim 10 and a method for clamping a component according to patent claim 11.

A large number of clamping devices for clamping and holding a component are known from the prior art.

One type of clamping device is, for example, a chuck, also known as a drill chuck, in which the component to be fixed is clamped between a plurality of displaceable clamping jaws. Such a clamping device has the advantage that the fixed components can be well centered between the clamping jaws. Such a clamping device comprising clamping jaws is usually used to fix rotating components, for example in drilling machines for clamping a drill bit or for clamping a milling machine.

Another known clamping device is a mandrel. A mandrel is inserted into a workpiece holder and has movable elements which press against the workpiece holder from the inside.

In order to clamp the component in the clamping device, the corresponding clamping means, such as the clamping jaws or the individual elements of a mandrel, can be displaced between a clamping position in which the component is clamped and a release position in which the component can be removed from the clamping device. The clamping means can be driven in different ways. Manual drives are known here, for example via screws that are to be tightened manually, as well as hydraulic and pneumatic drives.

The underlying object of the invention is to provide a clamping device and a sensor with such a clamping device and a method for clamping a component, by means of which high clamping forces can be generated in the simplest possible way.

The object is achieved according to the invention with the features of the independent claims. Further practical embodiments and advantages are described in connection with the dependent claims.

A clamping device according to the invention for clamping and holding a component comprises at least one movable clamping element for contact with the component. The clamping element can be moved between a clamping position and a release position by means of a drive device. The clamping position corresponds to a position of the at least one clamping element in which the component is clamped and fixed. In the clamping position of the clamping device, the component can be machined or the component itself can be used to machine a workpiece. The loose position allows the component to be removed from the clamping device.

A component can be any object that can be gripped by clamping elements and held by them. Depending on the arrangement of the clamping elements, the clamping devices can be used to hold components of different geometries (round, cylindrical, angular) both on the outside and on the inside.

In order to move the at least one clamping element between the clamped position and the released position, the drive device comprises a drive element made of a shape-memory material.

Depending on the temperature or a magnetic field, a shape-memory material has two different structures, with the conversion between the two structures being accompanied by a change in shape of the drive element made of the shape-memory material. The change in shape can then cause a movement of a tensioning element coupled thereto.

The temperature-dependent phase transformation is usually a transformation between the crystal structures of martensite and austenite. The austenite crystal structure is present at higher temperatures and the martensite crystal structure at lower temperatures. The crystal structures or phases can change into one another as a result of temperature changes (two-way effect). The shape-memory material is able to deform back into a shape that was previously impressed—for example, by severe deformation. The phase transformation is reversible.

The change induced by a magnetic field is usually a change in length. The material reorients itself in the ferromagnetic martensitic phase due to the mobility of the twin boundaries in the atomic lattice. Since the martensitic structure is tetragonal, such a microscopic change in orientation also results in a macroscopic change in length of such a sample. This reorientation can be caused by external forces (simple pressing on an axis) or due to anisotropic permeability (direction-dependent magnetic conductivity) through an external magnetic field.

The materials mainly used as shape memory alloys are metallic alloys such as NiTi (nickel-titanium) and NiTiCu (nickel-titanium-copper) or single-crystal alloys of nickel, manganese and gallium. However, shape-memory plastics such as shape-memory polymers can also be used.

Overall, the advantageous properties of a shape memory material are used here in order to drive a tensioning element with the shape memory material. During a phase transformation of the tensioning element, the outer shape of the drive element can change in such a way that the drive element performs a stroke that is transmitted to the tensioning element.

Due to the high energy density of the shape-memory material during a conversion between the two phases, it is possible to realize very high clamping forces with a low weight of the drive element at the same time.

As already mentioned above, the drive device can be operated with the drive element made of a shape memory material as a function of the temperature. Depending on the temperature, the drive device performs a stroke and moves the at least one clamping device. The advantage of a temperature-dependent drive is that the clamping process can be automated very well, since the temperature is defined via temperature measuring devices, heating and cooling and can be set and controlled quickly.

The clamping device can also be driven by applying an external magnetic field. The shape-memory material then exerts a stroke as a function of a magnetic field.

In particular, the drive element made of the shape memory material is designed as a spring, in particular as a helical spring. The coil spring is compressed (tightened) in the first phase of the shape memory material and relaxed in the second phase of the shape memory material. The change between the tensioned and the relaxed state of the spring then causes a displacement of the tensioning element.

Depending on the design of the tensioning device, the tensioning element is in the released position when the spring is compressed or when it is relaxed. Corresponding examples are also explained below in connection with the figures.

It is advantageous if the clamping element is in a clamped position at a first temperature and in a released position at a second temperature, the second temperature being higher than the first temperature. In particular, the first temperature is an ambient temperature that is usual for the area of use of the component, usually room temperature. The second temperature is higher than the first temperature and is only reached when the component is in use by the external supply of heat. In other words, this means that no heat supply is necessary during the period in which the component is clamped and operated or processed, and the temperatures prevailing there also do not lead to activation of the drive element. A phase transformation of the drive element and thus a movement of the clamping elements into a loose position is only brought about by the targeted supply of heat. For clamping elements, which move by tightening and relaxing a spiral spring, this means that they only move into the loose position under the influence of sufficient temperature. On the one hand, such a clamping device is operated in a particularly energy-saving manner and, on the other hand, it is particularly safe, since the component is held independently of an external supply of heat.

In a practical embodiment of a clamping device according to the invention, the at least one movable clamping element is a clamping jaw. In particular, the clamping device has a plurality of clamping elements in the form of clamping jaws, preferably three or more clamping jaws. The clamping jaws are used to rest on the component and have a contact surface with a geometry adapted to the component. In the case of components with a circular outer contour, the clamping jaws are arranged in a circle around the component and the clamping jaws each have a contact surface that extends over part of an arc of a circle. Other outer contours of components are also conceivable, with the number and arrangement of the clamping jaws and the geometry of the contact surfaces being adjusted accordingly.

In particular, the at least one clamping jaw is connected to an abutment via the drive element. A relative movement of the clamping jaw with respect to the abutment is then realized by the stroke induced with the drive element made of shape memory material.

The drive element preferably connects the abutment and the clamping jaw directly. In particular, a spring is used as the drive element, which extends from a rear side of the clamping jaw opposite the contact surface to the abutment extends. The direction of the clamping force exerted by the clamping jaws on the workpiece corresponds in particular to the direction of the stroke of the drive element.

In a particularly safe embodiment, the springs are arranged in such a way or the phase transformation takes place in such a way that the springs are relaxed at typical operating temperatures of the component and tension the tensioning elements against the component and contract and tension under the influence of external heat, so that the tensioning elements move into the loose position proceedings.

In an alternative embodiment, the clamping element is a slotted sleeve. The slotted sleeve has one or more slots distributed over the circumference of the sleeve, which allow the sleeve to be compressed uniformly and the diameter of the sleeve to be correspondingly reduced. The sleeve is arranged in a receiving device. A receiving device is a device which has a cylindrical opening for receiving the sleeve. The sleeve and the receiving device each have wedge-shaped geometries that correspond to one another, so that the sleeve is compressed in the radial direction when it moves into the receiving device. When the sleeve moves axially, the two wedge-shaped side faces of the sleeve and the receiving device slide off one another, as a result of which the sleeve is pressed together. The wedge-shaped geometries each extend in particular at one end of the sleeve or the receiving device. The sleeve widens at one end in the radial direction and the opening of the receiving device also widens in a wedge shape in the radial direction.

The opening in the sleeve serves to accommodate the component to be held and fixed. The component then rests against an inside of the sleeve. The compressed state of the sleeve corresponds to the clamping position in which a clamping force is exerted on the component in the radial direction. In the loose position, the slots of the sleeve are not compressed and the component can be removed from the sleeve.

In particular, the drive unit with the at least one drive element serves to move the sleeve axially in the receptacle. The drive element is arranged in particular with one end on an end of the sleeve which is arranged in the opening of the receptacle and is supported on a wall of the receptacle, in particular on the bottom of the opening. The axial stroke of the drive element causes the sleeve to be compressed and converted into a radial clamping force. The at least one drive element is preferably a spring.

For an alternative, particularly safe embodiment, the springs are preferably arranged in such a way, or the phase change takes place in such a way that the springs are tensioned at typical operating temperatures of the component and pull the sleeve into the opening of the receiving device. The springs relax as a result of an external heat influence and the sleeve is moved in the axial direction out of the opening of the receiving device into the loose position.

In an alternative embodiment, the drive element made of the shape-memory material can be designed as a wire, preferably as a tension wire. Such a wire can transfer the tensioning element from the tensioned position to the release position, for example against the force of a spring, in particular a compression spring designed as a helical spring, and according to one of the above-mentioned Activation methods are activated.

For this purpose, the tensioning element can be designed, for example, as a tensioning mandrel or a bolt. Such a mandrel or clamping bolt can, for example, lock a housing, in which case the locking can then be released by activating the drive element.

The invention also relates to a sensor with a clamping device as described above. The sensor is in particular a sensor for measuring a fill level, a limit level or a pressure.

For example, a fixture can be used as a process connection used to attach the sensor to a vessel or pipe. In particular, embodiments of clamping devices are preferred here which have a clamping position under the operating temperatures of the sensor and which, under the effect of heat, change into a loose position for removing the sensor.

It is also conceivable to use the tensioning device as protection against theft or manipulation. Alternatively, the tensioning device can serve as a cover closure, with the cover being fixed relative to a housing of the sensor.

It is also conceivable to use the clamping device to fix lines, for example cables. Accordingly, the tensioning device can be used, for example, in cable glands and/or cable bushings.

Furthermore, the invention relates to a method for clamping a component. In this case, a movable clamping element is moved between a clamping position and a release position by means of a drive device, the drive device comprising a drive element made of a shape-memory material. A particularly efficient displacement of the tensioning element can be brought about by the phase transformation of the drive element made of the shape-memory material.

Shape memory materials have a high energy density, so that large strokes or heavy loads can be realized even with a low weight of the drive element.

In particular, due to a change in temperature and/or a change in magnetic field, a movement of the tensioning element is effected. The temperature or a magnetic field can be set in a controlled manner and the process can be well controlled.

• 1 eine erste Ausführungsform einer erfindungsgemäßen Spannvorrichtung in einer Losstellung in einer schematischen Darstellung in einer Draufsicht,
• 2 die erste Ausführungsform der Spannvorrichtung aus 1 in einer Spannstellung in einer schematischen Darstellung in einer Draufsicht,
• 3a eine zweite Ausführungsform einer erfindungsgemäßen Spannvorrichtung in einer Losstellung in einer schematischen Darstellung in einem Querschnitt,
• 3b die zweite Ausführungsform einer erfindungsgemäßen Spannvorrichtung in einer Losstellung in einer schematischen Darstellung in einem Querschnitt gemäß Linie IIIb-IIIb aus 3a,
• 4a die zweite Ausführungsform einer erfindungsgemäßen Spannvorrichtung in einer Spannstellung in einer schematischen Darstellung in einem Querschnitt,
• 4b die zweite Ausführungsform einer erfindungsgemäßen Spannvorrichtung in einer Spannstellung in einer schematischen Darstellung in einem Querschnitt gemäß Linie IVb-IVb aus 4a, und
• 5 eine alternative Ausgestaltung einer Spannvorrichtung mit einem Spanndorn.

Further practical embodiments and advantages are described in connection with the figures. Show it:

• 1 a first embodiment of a clamping device according to the invention in a loose position in a schematic representation in a plan view,
• 2 the first embodiment of the clamping device 1 in a clamping position in a schematic representation in a plan view,
• 3a a second embodiment of a clamping device according to the invention in a loose position in a schematic representation in a cross section,
• 3b the second embodiment of a clamping device according to the invention in a loose position in a schematic representation in a cross section according to line IIIb-IIIb 3a ,
• 4a the second embodiment of a clamping device according to the invention in a clamping position in a schematic representation in a cross section,
• 4b the second embodiment of a clamping device according to the invention in a clamping position in a schematic representation in a cross section according to line IVb-IVb 4a , and
• 5 an alternative embodiment of a clamping device with a mandrel.

In the 1 and 2 a first embodiment of a clamping device 10 is shown in a view from above.

The clamping device 10 here comprises three clamping elements 12 in the form of clamping jaws 14, each of which has a contact surface 16 extending over an arc. The clamping jaws 14 are used here to hold and fix a component 18 with a circular outer contour. The clamping jaws 14 are arranged equidistant from one another in a circle around the component 18 .

The component 18 could be a sensor with a cylindrical housing, for example.

A drive device 20 connects to the back of the clamping jaws 14, with the drive device 20 here in each case comprising a drive element 22 made of a shape-memory material. The drive element 22 is designed here as a spiral spring 24 and extends from the back of the respective clamping jaws 14 to an abutment 26.

As in a synopsis of 1 and 2 is clearly recognizable, the clamping jaws 14 are between a loose position ( 1 ) and a clamping position ( 2 ) relocatable. In the loose position, the clamping jaws 14 are arranged with their contact surfaces 16 at a distance from the component 18 and the component 18 can be removed from the clamping device 10 . In the clamped position, the clamping jaws 14 rest against the component 18 with their contact surfaces 16 and the component 18 is fixed between the clamping jaws 14 .

The shifting of the clamping jaws 14 between the clamped position and the released position is effected by means of the drive elements 22 . In the release 1 the spiral springs 24 are tensioned (contracted). The clamping jaws 14 are retracted outwards in the radial direction in the direction of the abutment 26 . In the clamping position in 2 the spiral springs 24 are relaxed and clamp the clamping jaws 14 against the component 18.

The tensioning and relaxation of the springs 24 made of the shape-memory material is brought about here by means of the effect of temperature. In the clamping position ( 2 ) there is a normal ambient temperature for the use of the component 18 . In order to now move the clamping jaws 14 into a loose position for removing the component 18, heat is supplied to the clamping device 10 (indicated by arrows 28). At a temperature greater than the transition temperature, the springs 24 transform to the previously imprinted shape of the contracted spring.

In this embodiment, the direction of the stroke of the drive element 20 and the direction of the tensioning element 12 are on the Component 18 exerted clamping force on an axis - here in the radial direction.

In connection with the 3 and 4 a second embodiment is described below, with the same reference numbers being used for components that are identical or at least functionally the same as for the description of the first embodiment.

For the second embodiment of a clamping device 10, a slotted sleeve 30 with slots 32 distributed over the circumference of the sleeve 30 serves as the clamping element 12 (cf. 3b ). The sleeve 30 has an opening 34 which serves to receive a component 18 . Here the sleeve 30 is designed as a hollow cylinder and the component 18 is also designed in the shape of a cylinder with a circular outer contour.

The sleeve 30 is arranged in an opening 36 of a receiving device 38 . In the present case, the sleeve 30 widens at one end in the manner of a truncated cone and has a side face 40 which extends outwards in the shape of a wedge. Correspondingly, the opening 36 in the receiving device 38 widens outwards in the radial direction and has a wedge-shaped inner surface 42 .

If the sleeve 30 now moves in the axial direction relative to the receiving device 38 into the opening 36, the wedge-shaped side surface 40 and inner surface 42, which are designed to correspond to one another, cause the sleeve 30 to be compressed and the slots 32 in the sleeve 30 to narrow (cf. 4b ).

A corresponding clamping position in the 4a and 4b shown. The sleeve 30 has a smaller diameter and is clamped against the component 18 .

A displacement of the clamping element 12 between the release position ( 3a and 3b ) and the clamping position ( 4a and 4b ) is realized by means of several drive elements 22 in the form of springs 24 made of shape memory material. The springs 24 are arranged at the lower end 46 of the sleeve 30 facing the bottom 44 of the opening 36 in the receiving device 38 and extend between the end 46 of the sleeve 30 and the bottom 44 of the opening, the bottom 44 of the opening 36 here being abutment is used.

The sleeve 30 is moved into the opening 36 by a contraction of the springs 24 and a radial clamping force is exerted on the component 18 . Correspondingly, when the springs 24 relax, the sleeve 30 moves out of the receiving device 38 and the sleeve 30 relaxes again.

In contrast to the first embodiment, it is provided for the second embodiment that the relaxation of the springs 24 is brought about by the influence of heat (indicated by arrows 28). This also means that the release position is reached under the influence of heat and the clamping position is at ambient temperature.

In this second embodiment, the linear stroke of the springs 24 is converted into a radial clamping force by the interaction of the sleeve 30 and the receiving device 38 .

5 shows an alternative embodiment with a mandrel 15, which can be used, for example, to lock a lid of a container or a field device, such as a sensor. The mandrel 15 is biased into a position by means of a compression spring 25 designed as a helical spring, in which the mandrel can latch or engage, for example, in a trap. By means of a drive element 22 designed as a tensioning wire 23, the mandrel 15 can be pulled back against the spring force and the lock can be opened.

Reference List

10

clamping device

12

clamping element

14

clamping jaws

15

mandrel

16

contact surface

18

component

20

drive device

22

drive element

23

tension wire

24

coil spring

25

spring, compression spring

26

abutment

28

arrow (heat)

30

sleeve

32

slot

34

opening

36

opening

38

recording device

40

side face

42

Inner surface

44

floor

46

end of the sleeve

Claims (13)

Clamping device (10) for clamping and holding a component (18), with at least one movable clamping element (12) for contact with the component (18), wherein the clamping element (12) can be moved between a clamping position and a release position by means of a drive device (20). is characterized in that the drive device (20) comprises a drive element (22) made of a shape memory material. Clamping device (10) according to the preceding claim, characterized in that the drive element (22) is designed as a spring (25) from the shape-memory material. Clamping device (10) according to one of the preceding claims, characterized in that the drive element (22) exerts a stroke depending on the temperature and/or an external magnetic field. Clamping device (10) according to the preceding claim, characterized in that the clamping element (12) is in a clamped position at a first temperature and in a loosened position at a second temperature, the second temperature being higher than the first temperature. Clamping device (10) according to one of the preceding claims, characterized in that the at least one movable clamping element (12) is a clamping jaw (14). Clamping device (10) according to the preceding claim, characterized in that the at least one clamping jaw (14) is connected to an abutment (26) via the drive element (22) made of the shape-memory material. Clamping device (10) according to any one of the preceding Claims 1 until 4 , characterized in that the clamping element (12) is a slotted sleeve (30) which is arranged in a receiving device (38) and wherein the sleeve (30) and the receiving device (38) each have mutually corresponding wedge-shaped geometries, so that the sleeve (30) is compressed in the radial direction during a movement into the receiving device (38). Clamping device (10) according to the preceding claim, characterized in that the sleeve (30) can be moved axially in the receiving device (38) by means of the drive unit. Clamping device (10) after claim 2 , characterized in that the drive element (22) is formed from the shape memory material as a tension wire (23). Clamping device (10) after claim 9 , characterized in that the clamping element (12) is designed as a mandrel (15). Sensor with a clamping device (10) according to one of the above Claims 1 until 10 . Method for clamping a component (18), in which a movable clamping element (12) is moved between a clamping position and a release position by means of a drive device (20), characterized in that the drive device (20) comprises a drive element (22) made of a shape memory material. Method according to the preceding claim, characterized in that the shape-memory material causes the clamping element (12) to move as a result of a temperature change and/or a change in the magnetic field.

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