SIGNAL

The invention relates to a vibration element for producing a haptic feedback signal, having the features of the preamble of claim 1.

Haptic feedback elements, which are referred to herein as vibration elements, are used in various applications to provide feedback to a user by way of vibration. Specifically, such vibration elements are used in operating elements, for example in buttons, in particular in travel-free buttons, to provide the user with feedback about the activation of the operating element.

Such vibration elements are mass-produced goods, where low costs with, at the same time, high technical functionality and reliability are extremely important. Here, against the background of the desired applications, a configuration with the smallest possible size and a sufficiently strong haptic signal, i.e. a sufficient vibration, so as to provide the user with reliably detectable feedback, are also desirable qualities. WO 2012/061495 Al discloses a vibration element with a piezoelectric bending transducer, wherein the bending transducer is mounted at its opposite end regions. Additionally, a mass is connected to the bending transducer, said mass influencing the vibration frequency and the amplitude of the deflection of the bending transducer.Proceeding herefrom, the invention is based on the object of facilitating a cost-effective, small-sized vibration element, in which, furthermore, the bending transducer preferably may be actuated with an acceleration that is as high as possible.

According to the invention, the object is achieved by a vibration element for producing a haptic feedback signal, comprising a piezoelectric bending transducer mounted in a housing, having the features of claim 1. In general, the bending transducer extends in the longitudinal direction and is directly or indirectly connected to a centrifugal mass, i.e. a mass moving or tending to move away from a centre, i.e. an oscillating mass. Here, the centrifugal mass comprises, consists essentially of or consists of hard metal. The term "comprising" as used herein can be exchanged for the definitions "consisting essentially of or "consisting of. The term "comprising" is intended to mean that the named elements are essential, but other elements may be added and still form a construct within the scope of the claim. The term "consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. The term "consisting of closes the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith.

In general, hard metal is understood to mean sintered cemented carbides, typically tungsten carbide, but also, e.g. vanadium carbide, titanium carbide, etc. Here, such hard metals mainly have the cemented carbide and, additionally, a binder. Cobalt, in particular, is used as a binder in this case. Here, the component of the cemented carbide or the mixture of various cemented carbides is typically between 90 and 95 wt%. The rest is the binder.

An advantage of using a hard metal is that it has a very high density which, typically, lies in the range between 6 and 15 g/cm ³ . As a result of this high density, it is therefore possible to fasten a large mass to the bending transducer in a very small space. This configuration is based on the idea that a centrifugal mass that is as large as possible is of particular advantage for the desired vibrations since this allows the frequency and amplitude to be shifted into a suitable range, even in the case of small-sized elements, such that the (body-borne) sound vibrations produced by the bending transducer are transferred to the housing and, hence, a perceivable vibration signal is produced.

The use of hard metal is furthermore based on the idea that hard metal is significantly more cost-effective in comparison with other materials of a comparable density. Hence, the use of hard metal as a centrifugal mass allows a particularly cost-effective, small-sized vibration element to be produced. The vibration element is installed into, e.g. an operating element, specifically a button, for producing a haptic feedback signal for a user.

In view of the sought-after low costs, it is furthermore advantageous that, during the production of the centrifugal mass, the latter is formed by a compression moulding process with a subsequent sintering process. Therefore, post-processing by, e.g. machining, which is cost-intensive, is not required.

Preferably, the centrifugal mass is U-shaped when viewed in the cross section perpendicular to the longitudinal direction such that a longitudinal groove is formed, in which the bending transducer lies. Therefore, the bending transducer is hemmed in by the lateral U-limbs of the centrifugal mass. Overall, the bending transducer is therefore surrounded by the centrifugal mass on at least three sides. The bending transducer is usually embodied as an elongate, plate-shaped element in a manner known per se. The two U-limbs of the centrifugal mass enclose the longitudinal sides of the bending transducer therebetween. Here, apart from a tolerance gap, the width of the longitudinal groove preferably corresponds to the width of the bending transducer. This configuration serves the purpose of arranging a mass that is as high as possible in the tightest possible space.

The same goal is served by a preferred development, according to which the centrifugal mass extends "at least substantially" over the whole length of the bending transducer. Here, at least substantially is understood to mean that the bending transducer has a mounting and/or connection region for an electrical connector, at least at one end region and preferably at both end regions thereof, and that the centrifugal mass extends over the whole length of the bending transducer and, preferably, these mounting and/or connection regions are not covered by the centrifugal mass.

Expediently, the bending transducer is only connected to the centrifugal mass in a, preferably, single support region. Here, in particular, the support region is only arranged centrally. Away from this support region, the bending transducer is spaced apart from the centrifugal mass such that the bending transducer has a free space for vibrations available away from the support region such that the bending transducer may vibrate in the direction of the centrifugal mass.Expediently, the centrifugal mass has a base with an elevated support region to provide this free space for vibration of the bending transducer. In particular, the base is the base of the introduced longitudinal groove here and is referred to hereinbelow as "groove base".

Expediently, the groove base is bent when viewed in a longitudinal section such that an a preferably uniform, continuous reduction in the base thickness to the two ends of the groove proceeding away from the support region is achieved. As a result of this, the free space for vibrations for the bending transducer is continuously widened proceeding from the preferably centrally arranged support region. Instead of a bent groove base, the latter alternatively can be obliquely inclined. In both cases, the groove base tapers to the ends thereof, proceeding from the support region. Preferably, this tapering is at a comparatively small angle of a few degrees, in particular, e.g. at an angle of 1° to 5° and preferably in the region of approximately 2° to 3°. In accordance with a preferred configuration, the bending transducer is connected indirectly to the centrifugal mass via a receiving component. By means of the receiving component, the bending transducer is positioned and centred relative to the centrifugal mass, preferably in a defined position. Therefore, preferably, the receiving component is a centring piece. Expediently, the receiving component is fastened centrally to the centrifugal mass. Overall, the receiving component facilitates simple, defined indirect fastening of the bending transducer, e.g. by way of adhesive bonding. Here, the receiving component preferably consists of an insulating material, in particular plastic. Furthermore, preferably the receiving component forms a single support region. In conjunction with the electrically insulating property, this forms a reliable electrical separation between bending transducer and centrifugal mass. This arrangement reduces the risk of a short circuit and also ensures a potential- free centrifugal mass.

For fastening purposes, the receiving component is preferably inserted into a recess in the centrifugal mass, for example snapped-in with form fit and/or adhesively bonded.

Expediently, the receiving component has a U-shaped embodiment; i.e., it has a base and two side limbs, between which the bending transducer lies. Preferably, the two side U-limbs are flush (apart from a tolerance gap), at least with the outer sides of the bending transducer, with the side limbs of the U-shaped longitudinal groove of the centrifugal mass.

Here, the base and/or the inner sides of the side limbs of the receiving component preferably project slightly over the base of the centrifugal mass or the inner sides of the longitudinal groove such that the bending transducer is reliably held at least at a slight distance from the centrifugal mass.

In an expedient development, the bending transducer is mounted at the two opposite end regions thereof on the housing, preferably in a movable bearing in each case.

In order to obtain targeted damping of the resonant frequency of the bending transducer, mounting on the housing is brought about by way of a damping element. In particular, the damping element reduces the resonant frequency of the bending transducer such that it is not too high for the sought-after haptic feedback signal.

Here, preferably, an O-ring made of an elastic material is used as a damping element. Therefore, in a preferred variant, an O-ring is attached in each case on both sides at the opposite mounting regions, by means of which the bending transducer is mounted in the housing.

The mounting on the housing by way of a damping element is a particularly critical region since the produced vibrations are thereby transferred onto the housing thereby. In comparison with, e.g. adhesive points, etc., the use of O-rings was found to be particularly simple and reproducible and cost-effective and easy to assemble. Moreover, the desired high acceleration of the piezoceramic is achieved by the mounting between the two O-rings.

Here, the damping elements, specifically the O-rings, preferably have a Shore A hardness in the range from 30 to 100.

In contrast thereto, the housing has a significantly harder material and, in particular, is made of plastic, for example polyamide, e.g. PA6 and in particular (glass) fibre reinforced polyamide, for example PA6GF 30.

In view of a configuration that is as cost-effective as possible, the bending transducer is a monomorph-type bending transducer. Therefore, the bending transducer only has a passive carrier layer, on which a piezoceramic has been applied only on one side. Here, the passive carrier layer is, for example, a plastic layer which, in particular, is fibre reinforced, for example by means of glass fibres or carbon fibres. In principle, other materials may also be used for the carrier layer. It is important that the coefficients of thermal expansion of the piezoceramic and of the passive carrier layer are at least similar.

Expediently, use is preferably made here of a (single) piezoceramic element or of only two piezoceramic elements. This promotes the production of high accelerations when the bending transducer deflects.

In view of the sought-after high acceleration values, an expedient configuration furthermore provides for a control unit to be assigned to the bending transducer which actuates the latter by way of voltage source in such a way that the bending transducer is only operated in one pole direction. This is understood to mean that no active AC voltage is applied to the bending transducer, i.e. that a negative voltage and a positive voltage are not alternately applied to the bending transducer, which negative and positive voltages would each lead to the deflection in the one direction or the other direction. Rather, actuation of the bending transducer is only effected in one direction, that is to say, e.g. with a positive pulse or only with a negative voltage pulse, in a periodically recurring fashion.

In view of the sought-after high acceleration values, provision is therefore expediently made for the bending transducer only to have applied thereto a half- wave of an, e.g. sinusoidal or rectangular supply voltage (AC voltage), or any other AC supply voltage, and for, subsequently, the bending transducer to be discharged again after each half-wave, as it were by way of a short circuit. This is preferably carried out by way of a discharge resistance, which lies, for example, in the range between 1 kQ and 50 kQ.

Furthermore, the bending transducer is expediently actuated by the system frequency, i.e. by the resonant frequency of the unit made from the bending transducer, the centrifugal mass and further elements optionally coupled thereto, such as, e.g. operating elements.

Preferably, the housing surrounds the bending transducer with the centrifugal mass fastened thereto and houses these. This is understood to mean housing of the bending transducer with the centrifugal mass which is closed on at least 2 or 3 sides. Preferably, the housing is only open to one side by means of which the bending transducer may be inserted laterally, i.e. in a direction across the longitudinal direction, together with the centrifugal mass. Here, the housing has a receptacle, the geometry of which is preferably matched to the dimensions of the bending transducer with the centrifugal mass fastened thereto, i.e. the bending transducer with the centrifugal mass fastened thereto lies with precise fit in the housing, apart from tolerance gaps.

In particular, the configuration of the vibration element described here offers the following advantages: - The use of hard metal, in particular by enclosing the bending transducer with the hard metal, allows minimal dimensions to be achieved;

- The mounting in O-rings has low damping properties and is reproducible;

- The use of a monomorph allows high acceleration values to be obtained; - The application of only a half-wave and the use of a discharge resistor, which short-circuits the piezoceramic charged by the half-wave, likewise promotes the desired high acceleration; and

- The insulating receiving component achieves simplified, defined positioning, the avoidance of short circuit and a potential-free centrifugal mass.

An exemplary embodiment of the invention is explained in more detail below on the basis of the accompanying drawings, in which:

Figure 1 shows a side view of a vibration element;

Figure 2A shows a plan view of a centrifugal mass;

Figure 2B shows a side view of an end side of the centrifugal mass in accordance with Figure 2A;

Figure 2C shows a cross-sectional view of the centrifugal mass along the section

A- A in accordance with Figure 2B;

Figure 3 A shows a plan view (side view) of a housing;

Figure 3B shows a cross-sectional view through the housing along the cut line B- B in accordance with Figure 3 A;

Figure 4 shows a schematic, very much simplified circuit diagram for illustrating the actuation of the bending transducer only with half- waves and the discharge by way of a discharge resistor;

Figure 5 shows a perspective exploded illustration of a further embodiment variant with a receiving component; and

Figure 6 shows the further variant in accordance with Figure 5 in the assembled state.

In the Figures, parts with the same effect have been provided with the same reference signs.

The vibration element 2 has a housing 4 with a bending transducer unit 6 lying therein. Here, as essential components, the bending transducer unit 6 comprises a bending transducer 8, which extends along a longitudinal direction 10, and a centrifugal mass 12. Here, the centrifugal mass 12 comprises hard metal and surrounds the bending transducer 8 over virtually the entire length thereof. Here, the centrifugal mass 12 overall extends over a length of at least 80% or at least 90% of the total length of the bending transducer. The bending transducer 8 has mutually opposing end regions 14, at which it is mounted on the housing 4 by way of damping elements 16. Here, in particular, the damping elements 16 are embodied as O-rings. Therefore, the end regions 14 form mounting regions. In the exemplary embodiment, one of these end regions 14 is simultaneously embodied as an electrical connection region, at which control lines 18 for actuating the bending transducer 8 are connected. During operation, the control lines 18 are connected to a control unit 20 for actuating the bending transducer 8.

The bending transducer 8 is preferably embodied as a monomorph-type bending transducer and has an inactive carrier layer 8A, on which preferably a single piezoceramic 8B has been applied to only one side in a manner known per se. To the extent that reference is made to "a" piezoceramic 8B in the present case, this is understood to mean an integral element which consists entirely of a piezoceramic material. As an alternative to the use of only one piezoceramic 8B, use may also be made of two piezoceramics 8B which are arranged, e.g. stacked over one another. Here, the respective piezoceramic 8B is actuated in a manner known per se by way of suitably embodied electrodes which, for example, are attached over the whole area on a flat side of the respective piezoceramic 8B.

The housing 4 has a cutout (or recess) 22 which is matched to the geometry of the bending transducer unit 6. Therefore, the cutout 22 is formed, in particular, by a central cuboid which is adjoined on both sides by respective holding slits for the end regions 14. Furthermore, recesses are arranged perpendicular to these bearing slits, said recesses being provided to receive the respective damping element 16.

Additionally, Figure 1 furthermore depicts a fastening region 24, at which the centrifugal mass 12 is connected to the bending transducer 8 either directly or indirectly by way of a receiving component 40 (in this respect, cf. Figure 5). In particular, this is achieved by adhesive bonding using a suitable adhesive.

The centrifugal mass 12 itself is depicted in Figures 2A to 2C. When looked at in cross-section (in this respect, cf. Figure 2B), it has a U-shaped embodiment such that a longitudinal groove 26 is formed extending in the longitudinal direction 10. Said longitudinal groove has a groove base 28. In the exemplary profile, the groove base 28 - as emerges, in particular, from Figure 2C - has embodiment cross-section which drops off or tapers towards the longitudinal ends thereof, proceeding from an elevated support region 30. The groove base 28 tapers to the outside at an angle a, which is approximately 2.5° in the exemplary embodiment. In the embodiment variant of Figure 2, provision is made for the bending transducer 8 to be supported directly on the centrifugal mass 12 in the support region 30. The longitudinal groove 28 has a width which preferably corresponds to the width of the bending transducer 8 such that, apart from tolerance play, the latter lies with precise fit between the two U-limbs of the centrifugal mass 12.

The height of the longitudinal groove 28, to be precise as measured at the elevated support region 30, furthermore preferably corresponds to the thickness of the bending transducer 8 or it is slightly greater than the thickness of the bending transducer 8 such that it is ensured that the two U-limbs completely enclose the bending transducer 8 at the longitudinal end edges thereof. This also applies to the second variant in accordance with Figure 5, which has the receiving component 40.

Figures 3A, 3B show the housing in a side view and in a sectional view along the cut line B-B in accordance with Figure 3 A. As may be gathered herefrom, the housing has a total of three side walls and is only open towards one side. This open side may also be easily identified in Figure 1. The bending transducer unit 6 is inserted laterally, i.e. perpendicular to the longitudinal direction 10, by way of this open side.

In view of accelerations of the bending transducer 8 which are as high as possible, the latter, during operation, preferably only has a (positive) half-wave of a supply voltage 32 (AC voltage) applied thereto in each case. For the purposes of "discharging" the bending transducer 8 such that the latter therefore returns to its initial position, the piezoceramic 8 is, as it were, short-circuited by way of a discharge resistor 34.

A possible circuit diagram for such an actuation is shown in Figure 4. It shows a circuit diagram for the actuation of two piezoceramics 8B, which are represented as capacitors in this circuit diagram. Blocking diodes 36 are used in this circuit such that only (positive) half-waves of the AC voltages provided by the supply voltage 32 are applied to the bending transducer 8. As a result of this, the piezoceramic 8B, and hence the bending transducer 8, is deflected. Subsequently, the discharge process is carried out by way of the respective discharge resistor 34 such that the bending transducer 8 returns to the initial position again.

A second, particularly preferred configuration is depicted in Figures 5 and 6. The essential difference to the embodiment variant in accordance with Figures 2A-2C consists of the bending transducer 8 being connected indirectly to the centrifugal mass 12 by way of the aforementioned receiving component 40. The receiving component 40 is embodied as a plastic part. It lies in a recess 42 in the centrifugal mass 12.

The side limbs of the U-shaped longitudinal groove 26 are interrupted for the recess 42 and the groove base 28 preferably also has a depression.

In the assembled state, the receiving component 40 is inserted into and fastened, for example snapped-in or adhesively bonded, in this recess 42, in particular with a precise fit. The receiving component 40 itself has, in turn, a U-shaped embodiment with a central receptacle groove for the bending transducer 8. At the same time, the receiving component 40 forms the only support region 30 for the bending transducer 8 and, in particular, it is embodied in such a way that the bending transducer 8 is at least a small distance from the centrifugal mass 12, in such a way that direct contact between bending transducer 8 and centrifugal mass 12 is avoided. To this end, the base of the receiving component 40 is slightly elevated in relation to the groove base 28. Preferably, the inner sides of the U- limbs of the receiving component 40 also project to the inside, as may be gathered from, in particular, Figure 6. The bending transducer 8 is fastened to the receiving component 40, preferably by adhesive bonding.

The remaining features and configurations, as explained in relation to Figures 1-4, apply to the same extent to the second variant as well. Thus, the groove base 28, which drops off towards the outside, adjoins on both sides of the receiving component 40.

List of reference signs

2 Vibration element

4 Housing

6 Bending transducer unit

8 Bending transducer

8A Carrier layer

8B Piezoceramic

10 Longitudinal direction

12 Centrifugal mass

14 End region

16 Damping element

18 Control line

20 Control unit

22 Cutout (or recess)

24 Fastening region

26 Longitudinal groove

28 Groove base

30 Support region

32 Supply voltage

34 Discharge resistor

36 Blocking diode

40 Receiving component

42 Recess a Angle