KR101176671B1 - Electromechanical force transducer - Google Patents

Abstract

A plurality of resonating elements; A low rigidity member coupled between adjacent surfaces of at least two adjacent resonating elements; And a stub member that supports the resonator element and couples the transducer to a position at which a force is applied. A plate-shaped resonating element having a frequency distribution of modes in the operating frequency range of the transducer; And a stub member that couples the transducer to a position where a force is applied, the resonator element is supported, and the stub member is aligned such that a full body non-bending mode is applied to the resonator element.

Description

Electromechanical Force Transducer {ELECTROMECHANICAL FORCE TRANSDUCER}

FIELD OF THE INVENTION The present invention relates to electromechanical force transducers, actuators, exciters and such devices, in particular devices used in acoustic devices such as loudspeakers and microphones, for example. It is about.

The invention relates, in particular, to an electromechanical force transducer of the kind described in the applicant's international patent application WO01 / 54450, comprising one or more resonant elements having a frequency distribution of modes in the operating frequency range of the transducer or Relates to a beam. Such transducers are known as "distributed mode actuators" or abbreviated DMAs.

It is an object of the present invention to provide a transducer in which damping is provided such that the Q of the mode is reduced and the cancellation between modes is reduced to increase the softness of the acoustic pressure.

It is also an object of the present invention to improve the robustness of the transducer, for example to reduce the failure rate in drop or crash tests.

Another object of the present invention is to reduce the first resonant mode frequency of an actuator or transducer, for example a DMA transducer.

In a first aspect, the invention is a type of transducer in which a low stiffness layer is inserted between a plurality of resonant elements and bonded to adjacent surfaces of the plurality of resonant elements. Simply adding an attenuation layer to one side of the resonant element or beam provides low attenuation performance as the attenuation layer extends with the element as the size of the element surface changes. However, the use of a flexible reference layer, which is robust against changes in size, such as foil, on the opposite side of the damping layer, results in improved damping while shearing between the varying device surface size and the non-extension foil. If the reference layer can vary in size against the damping plane, the damping effect will be doubled. This is an effect obtained by attaching the damping layer between adjacent element faces.

In another aspect, the invention is a DMA transducer in which an out of plane DMA mode is applied to the audio band.

1 is a side view of a first embodiment of the electromechanical force transducer of the present invention.

2A is a partial side view of an electromechanical force transducer.

2B is a side view of a first embodiment of the electromechanical force transducer of the present invention.

3 is a graph comparing the blocked forces of a single beam transducer and the transducer of FIG.

4 shows the sound pressure between an undamped dual beam DMA, a half attenuated DMA (attenuated material adheres over half of the length of the resonant element) and a fully damped dual beam DMA transducer. Graph to compare.

5 is a side view of a single beam actuator.

6 is a side view of a second embodiment of the electromechanical force transducer of the present invention.

7 is a graph comparing block forces under different conditions.

8A is a graph comparing sound pressure under different conditions.

FIG. 8B is a perspective view of the transducer of the type shown in FIG. 6 mounted to a panel edge; FIG.

FIG. 9 is a graph comparing the blocked forces of different compliant stubs. FIG.

1 shows a dual beam transducer of the type described in WO01 / 54450 incorporated in the present invention. The transducer 1 comprises a first piezoelectric beam 2, by means of connecting means in the form of a rigid stub 4 located near the center of both beams the second piezoelectric beam 3 is connected to the first piezoelectric beam. It is mounted on the back of the beam 2. Each beam is bimorph.

The transducer 1 is mounted to a bending-wave loudspeaker panel structure such as a distributed mode loudspeaker (DML) by means of coupling in the form of a rigid stub 6 located near the center of the first beam.

In the present invention a low rigid layer 7 of foamed plastic is bonded between the adjacent surfaces of the two beams 2, 3. The adhesive layer may be discontinuous to cover the entirety of the adjacent surface or to attenuate certain modes, for example.

The following shows the parameters of the appropriate foam damping material, "poron" low rebound foam polyurethane plastic material.

Type: 4790-92-25041-04S

Thickness: 1.05mm (also succeeded by 1.0mm)

Density: 400kg / m3

Compressional E (Young's modulus of blowing agent in compression) = 2 MPa at 1 kHz

Measuring resistance, R is approximately 8 * 10 ⁵ Ns / m3.

This value is the measured real part of the mechanical resistance at compression, not at shear deformation. Shear strain values are not available.

In addition, the use of thin blowing agents (0.6 mm) gave good results. Thick foams up to 1.5 mm are also expected to give good results. A thickness limit between 0.3 and 2.0 mm is proposed.

Density (separated from E and R) is expected to be irrelevant, can vary by 100 times, and has little effect. E is important, but the occurrence of shearing makes it difficult to recognize the importance of E. A four-fold increase in E will begin to strengthen the beam and should be avoided. The reduction in E has little effect since the system stiffness is not greatly affected by the addition of blowing agent. The R value is important. Reducing R is expected to affect the attenuation linearly. It should not be reduced more than four times. Increasing R is good but cannot be obtained without affecting other parameters.

2 shows the effect of adhesion to one or both sides of a multiple beam transducer. 2A shows the case where the damping layer 7 is glued to only one beam 2. When the other beam 3 moves with respect to the beam 2, it slips on the upper surface of the damping layer and therefore neither deforms nor adds attenuation to the bending resistance. However, in FIG. 2B, the damping layer is bonded to both beams, so that shear deformation occurs due to the relative movement of the beam 3 relative to the beam 2. It is this shear strain that applies attenuation.

The beam lengths need not be the same, but if they are the same then the maximum attenuation effect is expected. The measurement effect of adding an attenuation layer between the two beams on the block force of the center mounted transducer is shown in FIG. 3. The Q of all modes is reduced and the natural frequency does not change, which means very low stiffness of the adhesive material 7. The addition of an attenuation layer increases the output when cancellation occurs within the transducer, such as between resonances of different length beams.

4 shows the simulation effect on sound pressure with added attenuation between the faces of a 36mm / 34mm beam length DMA transducer. The output at the transducer fundamental is slightly reduced, but a wider increase in output occurs in the 3-4 kHz range. The 3-4 kHz region where a wide range of output increase occurs is the region of internal cancellation in the transducer. Also, the sound pressure response is smoother.

Drop test failure rates are expected to decrease. Most of the energy in the collision will be in the exciter at the fundamental resonance. Since the damping reduces the Q of this resonance, the instantaneous maximum displacement will decrease and reduce the stress in the beam. This stress reduction is expected to improve drop test stability. In addition, the structural height of the transducer can be reduced by the present invention.

The stubs used to couple the transducers of the kind described above to the load are assumed to be rigid in all three parallel axes and the rotational stiffness is usually neglected and high. For the beam with the stub in the middle of its length, zero rotation occurs at the stub with respect to the beam fundamental resonance. If this zero rotation boundary condition is repeated at the end of a half length beam, the fundamental wave will occur with half the force at the same frequency as the full length beam. Referring to FIG. 5, this is a cantilever condition. 5 is a diagram showing a basic mode shape of the cantilever beam (offset stub). The deformed shape shows pure bending motion.

However, referring to FIG. 6, by reducing the stub rotational stiffness from this high value to a low value, the beam f0 decreases, becomes less dependent on the bending motion of the beam, and becomes more rigid. FIG. 6 is a diagram of the mode shape of a beam coupled to a panel with a soft stub that enables rotation of the beam, the mode shape showing constant bending and constant rotational deformation in the beam. In the limiting situation of rotational stiffness zero, the mode is reduced to 0 Hz, which is the rigid body mode. Reference 9 denotes a trapped air layer behind panel 5, which couples to the panel in the simulation, affects the set of resonance modes in the panel, and reference 10 denotes panel 5 and transducer ( Represents a body of a mobile phone including a loudspeaker formed by 1). The refraction of the beam 2 is very exaggerated to see well.

By selecting this rotational compliance, the beam f0 can be smaller than the beam's f0, which is twice the length mounted at its center, and referring to FIG. 7, an FE analysis was used to demonstrate this effect. 7 is simulated generated by three conditions: a 36 mm beam mounted at the center, a half length beam with a stiff stub at the end, and a half length beam with a compliant stub at the end. It is a graph of block force. Hard stubs cause stiffening of the beam and effectively reduce its length slightly.

A solid stub will have the same stiffness in three translational and rotational axes. By appropriately adjusting the cross-sectional shape of the stub, different stiffness can be produced in six different axes. As a result, modes on different axes occur at different frequencies. Referring to FIG. 8, if the load impedance is asymmetrical, the modes related to movement in a direction other than perpendicular to the beam surface can couple to the panel, providing increased mode density. 8A is a graph of simulation effects on sound pressure generated by varying stub stiffness. FIG. 8B is a perspective view of a panel shaped loudspeaker showing in-plane DMA movement with a panel 5 with an attached transducer mounted on a soft stub 6 in a one-beam cross section. . In the in-plane mode shown in FIG. 8, if the rotational stiffness around the axis 8 perpendicular to the face of the panel is ignored, this mode does not exist. If the first mode is due in part to the rotational stiffness around the axis along the short edge of the beam, the second mode is due to the stiffness around the axis perpendicular to the beam. Also, the last axis of rotation around the axis moving along the length of the beam will create a mode.

Referring to Figure 9, an example of a stub shape that provides different stiffness in different axes is an I-section. 9 is a graph of the simulation effect on block force of a polycarbonate I-section stub with varying vertical bar lengths. The width of the stub is the total 3mm plus the inner bars of 1mm width, and the bar length is shown in the graph.

By changing the fundamental resonance from pure bending in the beam to partial translation, the stress in the beam is reduced in the fundamental. Since the fundamental resonance receives most of the energy in a collision, the beam will not be damaged as most of the deformation takes place on the stub.

Although stubs of one-beam cross section have been presented, many other stub cross sections may be used, for example trapezoidal, cylindrical, or the like.

Claims (20)

As an electromechanical force transducer, A plurality of resonating elements; An attenuation layer coupled between the adjacent surfaces of the at least two adjacent resonance elements; And A stub member supported by the resonating element and coupling the transducer to a position at which a force is applied; The damping layer is selected such that the output is increased in the internal offset frequency region of the transducer. The method of claim 1, The damping layer is electromechanical force transducer, characterized in that made of foam plastic. The method of claim 2, And said foamed plastic has a low rebound characteristic. The method of claim 1, The damping layer is in the form of a layer bonded to all or a portion of an adjacent surface of the resonating element. The method according to any one of claims 1 to 4, And said resonating element is beam-like. The method according to any one of claims 1 to 4, The stub has a low rotational stiffness such that the fundamental resonance of the transducer becomes independent of the bending motion of the transducer and becomes similar to a rigid body. The method of claim 6, Wherein the stub has different stiffness in the translational and rotational axes such that modes in different axes occur at different frequencies. The method according to any one of claims 1 to 4, At least one of the parameters of the resonant element is selected to enhance the mode distribution of the element within an operating frequency range, wherein the parameter is selected from the group consisting of aspect ratio, flexural stiffness isotropy, thickness isotropy, and geometry Electromechanical force transducer, characterized in that. The method according to any one of claims 1 to 4, At least one of said resonating elements is an active element. The method according to any one of claims 1 to 4, And said damping layer is coupled over the entirety of said adjacent surface. As an electromechanical force transducer, A plate-shaped resonating element having a frequency distribution of modes in an operating frequency range of the transducer; And A stub member coupling the transducer to a position where a force is applied, The stub member has a low rotational stiffness such that the fundamental resonance of the transducer becomes independent of the bending motion of the transducer and is similar to a rigid body. The method of claim 11, wherein Wherein the stub member has different stiffness in the translational and rotational axes such that modes in different axes occur at different frequencies. The method of claim 11, wherein An electromechanical force transducer, characterized in that the cross-sectional shape of the stub is non-clrcular. The method of claim 13, The cross-sectional shape of the stub is an I-section. The method according to any one of claims 11 to 14, At least one of the parameters of the resonant element is selected to improve the mode distribution of the element within the operating frequency range, wherein the parameter is selected from the group consisting of aspect ratio, flexural stiffness isotropy, thickness isotropy, shape Electromechanical force transducer. The method according to any one of claims 11 to 14, An electromechanical force transducer, comprising a plurality of resonant elements having a frequency distribution of modes within an operating frequency range. The method according to any one of claims 11 to 14, And said at least one resonant element is an active element. The method according to claim 1 or 11, wherein And the resonant element has a frequency distribution of modes within an operating frequency range of the transducer. The transducer according to claim 1 or 11; And A loudspeaker comprising a bending-wave panel form acoustic radiator to which the transducer is coupled. delete

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