EP2030264A1

EP2030264A1 - Piezoelectric generator

Info

Publication number: EP2030264A1
Application number: EP07764392A
Authority: EP
Inventors: Klaus Reichmann; Igor Kartashev; Wolfgang Athenstaedt
Original assignee: Epcos AG
Current assignee: TDK Electronics AG
Priority date: 2006-06-21
Filing date: 2007-06-20
Publication date: 2009-03-04
Also published as: DE102006028534A1; WO2007147400A1; JP2009542169A; US20090146534A1

Abstract

The invention relates to a piezoelectric generator comprising a resonance system provided with a piezoelectric converter (2). Said generator comprises a feedback circuit (26) which is connected to the output of the piezoelectric converter (2) and used to adjust the oscillation frequency of the resonance system.

Description

description

Piezoelectric generator

A piezoelectric generator is z. B. from the document US 5,751,091 known. This generator is used in a clock.

An object to be solved is to provide a high-efficiency piezoelectric generator, which is characterized by a high mechanical stability.

A piezoelectric generator with a resonance system that can be excited to mechanical vibrations is provided, which comprises a piezoelectric transducer. The generator further includes a feedback circuit electrically connected to the piezoelectric transducer. The feedback circuit is provided for driving vibrations of the resonance system and in particular for adjusting the oscillation frequency of the resonance system.

The piezoelectric generator is suitable for the transformation of a mechanical energy into an electrical energy. The piezator can z. B. be realized for power supply in a portable electrical device. The mechanical energy used to excite the resonance system can be generated, for example, by body or air movements.

The piezoelectric transducer is suitable for converting the mechanical energy of the resonance system into an electrical energy that can be supplied to an electrical load, ie a consumer. Furthermore, advantageous embodiments of the piezogenerator will be described.

The piezoelectric transducer is referred to below as a piezo element.

The mechanical resonance system is preferably mechanically excited to vibrate during excitation phases. For this purpose, in a preferred embodiment, the generator comprises an excitation device which ensures the mechanical excitation of the resonance system during each excitation phase.

Mechanical parameters of the excitation system can be adjusted by means of the feedback circuit. The mechanical parameters of the excitation system are z. B. the predetermined rotational frequency or the speed of a transport device, which carries an activator explained below for exciting the resonance system. Thus, the frequency of action of the activator can be adjusted to the resonance system.

The generator has a start-up phase and a working phase, which corresponds to the normal operation of the generator. During a start-up phase, the resonance system is first brought out of balance spontaneously or by means of a starting device. This triggers mechanical vibrations of the resonance system, in which the piezoelectric element, an electrical signal is generated at a frequency that matches the natural frequency of the mechanical resonance system. A part of this signal is processed by the feedback circuit into a control signal and used to drive the excitation device of the resonance system. The feedback circuit is used during the start-up phase as a remedy to Oscillation of the resonance system provided in the operating state. The feedback circuit is preferably suitable for stabilizing the excitation frequency. The excitation frequency is the number of excitations of the resonance system per unit of time.

After the transient phase, the resonance system reaches a normal operating state. The normal operating state means mechanical vibrations of the resonance system preferably at a natural frequency (resonance frequency) of the resonance system. These vibrations are converted by the piezoelectric element into an electrical signal. The following describes how the generator works in normal operation.

The Z. B. by the piezoelectric element and the oscillating device described below formed mechanical resonance system is characterized by a natural frequency. This may be its fundamental frequency or a higher harmonic of the fundamental frequency. The natural frequency of the resonance system preferably agrees with an n-th harmonic of the excitation frequency u-b, where n is an integer and where n_> 1. It is advantageous to select the excitation frequency equal to the natural frequency of this resonance system. Where n = 1. The range of n between 2 and 5 may also be advantageous.

The controlled by the feedback circuit mechanical action (excitation) on the resonance system is preferably synchronized with the natural vibration of the resonance system with respect to the frequency, the phase and the amplitude, ie the intended maximum deflection. The resonance system is excited during an excitation phase, which is preferably at most half of the oscillation period T of the resonance system. The excitation phase can also be between T / 4 and T / 2 to last; to endure, to continue. The excitation phase is preferably synchronized with the oscillation phase, ie the maximum deflection with respect to the state of equilibrium is brought about at a time at which, without excitation, one of the amplitude maxima of the (damped) natural oscillation of the resonance system would occur.

The resonance system preferably comprises a vibration device which has oscillatable vibration elements, between which the piezoelectric element is clamped. The oscillating elements are preferably oscillatable against each other. It is advantageous if a plane in which the oscillating elements oscillate is aligned perpendicular to the direction of gravity. The oscillating elements can oscillate freely after an excitation phase in which they are deflected with respect to their rest position.

The oscillating device is preferably provided for generating a compressive stress on the piezoelectric element. The piezo element can, for. B. compressed by the compressive stress along a longitudinal direction. By means of the compressive stress but also a shear deformation of the piezoelectric element can be brought about. In the oscillations of the oscillating elements, the deformation of the piezoelectric element clamped in the oscillating device is effected. By means of the piezoelectric element, the mechanical energy of the vibrating device is converted into electrical energy.

The oscillating device is preferably provided for biasing the piezoelectric element. A prestressed piezoelectric element makes it possible to achieve a particularly high power density of the generator. In a preferred variant, the oscillating device has energy storage elements mechanically coupled to the oscillating elements. As energy storage elements for storing the (mechanical) energy in particular weights are suitable, which are attached to the vibrating elements, preferably in the region of the freely oscillatable ends of the vibrating elements.

The generator may include an energy reservoir, which is decoupled from the vibratory elements outside of the excitation phases, for storing energy that may be consumed for excitation of the resonant system, the power consumption being controlled by the feedback circuit. This energy can be supplied to the vibrating elements directly or with the aid of the activator. The stored energy in this reservoir can be converted into free or - when using the activator - forced vibrations of the vibrating device.

The energy reservoir for energy may be designed to be suitable for storing the energy of uncorrelated mechanical actions. Possible mechanical effects are z. B. uncorrelated vibrations of a carrier to which the vibrating device is attached. The energy of the air pressure (eg with breath and acoustic signals of the environment) can also be accumulated in the energy reservoir. The stored energy can z. B. are used to drive the transport device to which the activator is coupled. The activator removes energy from the energy reservoir and transfers it to the vibrating device during the excitation phase.

For energy storage z. B. compressed air suitable. The air pressure can be in a designated container z. B. be built by wind, breath or by squeezing a shoe sole while walking. The container may be inflatable like a balloon, wherein in the container preferably an overpressure protection is provided.

The container preferably has an inlet opening and an outlet opening. The inlet opening, through which the air can be pumped, is provided with a first valve. The outlet opening can be closed with an activator designed as a valve. The activator acts as a regulator for metered release of the stored energy. In this variant, a contactless regulated power transmission to the resonance system is possible. In this case, the air is metered and preferably let out of the container at a predetermined frequency. The resulting air flow can bring swinging components of the resonance system to vibrate.

Another way to store the energy is a mechanism with a wind-up spring.

The excitation device may comprise a metering device coupled to the energy reservoir for the metered delivery of the stored energy and an activator, which is preferably coupled to the metering device or -. B. when realized as a valve - forms at least a portion of the metering device. The metered delivery means z. B. a matched to the energy demand excitation intensity or excitation frequency. The metering device is characterized by mechanical parameters whose values can be changed by the feedback circuit. For this purpose, the dosing device is preferably coupled to the feedback circuit. For excitation of vibrations of the Oscillation device is a metered delivery of mechanical energy from an energy reservoir particularly advantageous.

The excitation device may comprise a transport device which is provided for transporting the activator. The transport device preferably has rotatable elements, the z. B. can be electromagnetically driven by control pulses of the feedback circuit. By the control pulses, it is possible to adjust the rotational speed of the rotatable elements. Thus, the speed and the frequency of action of the activator can be controlled to the resonance system.

The activator can be set in motion under the action of an external mechanical force. The activator preferably constitutes a wedge-shaped part which is used to excite vibrations of the oscillating device and which is provided for metered delivery of mechanical energy to the resonance system during periodic operation of the generator.

The activator preferably passes between the vibrating elements during an excitation phase and pushes them apart. With each pass of the activator, the energy stored in the weights is proportional to the deflection of the weights from the respective rest position. This energy can be converted into the energy of the free oscillations of the oscillating device after the intended maximum deflection, after the termination of the excitation phase. The excitation phase ends as soon as the activator leaves the area arranged between the weights. The length of stay of the activator in this area, ie the duration of the incentive tion phase, is chosen so that it is a maximum of half the oscillation period of the vibrating device.

The piezoelectric generator may comprise a rectifier which is electrically connected to the piezoelectric transducer. Thus, the AC voltage generated at the piezoelectric transducer can be rectified. The rectifier is preferably arranged between the piezoelectric transducer and the electrical load. The feedback circuit is preferably supplied with the rectified signal.

The piezoelectric generator may comprise an electrical storage element, which is preferably electrically connected to the piezoelectric transducer. As an electrical storage element is a z. B. grounded capacitor into consideration. The capacitor smooths the rectified, ripple-generating generator voltage. For charging an electrical storage element, a part of the rectified signal can be used. The electric charge accumulated on the electric storage element can be used to supply the voltage to the feedback circuit and to start the excitation device.

The oscillating elements each preferably have a fixed end and a free swinging end. Each vibrating element can, for. B. be a strip-shaped bending spring. The oscillating elements may, for example, form the legs of a U-piece, which is preferably fastened to a carrier in the region of its connecting piece. The oscillating device in a preferred variant has the shape of a tuning fork. The vibration (vibrations) of the wearer can cause the vibration device to vibrate freely. But the vibrating device can also by an air pressure to be made to swing. This can be achieved in both cases with or without the activator.

The transport device may in one variant comprise a conveyor belt which is set in motion by means of transport rollers. The transport rollers are preferably coupled to an aforementioned energy reservoir for mechanical energy. The transport device may alternatively comprise a rotating device in the form of a disc, a wheel or a ring, which is rotatable about an axis of rotation and to which the activator is attached, which passes through the rotation of the wheel between the vibrating elements and thereby pushing apart the Causes oscillating elements.

The piezoelectric element has electrodes and at least one piezoelectric layer which is arranged between the electrodes. The electrodes can z. B. external electrodes, which are arranged on the surface of a base body of the piezoelectric element. Between the outer electrodes, a piezoelectric layer is arranged. During the deformation of this piezoelectric layer, an electric charge is generated at the outer electrodes. The electrodes may also be internal electrodes, which are each arranged between two piezoelectric layers. Preferably, a plurality of internal electrodes are present, which are alternately connected to a first and a second outer electrode. For the piezoelectric layers, a ceramic with piezoelectric properties is very well suited.

The feedback circuit may comprise a comparator and / or an amplifier. A comparator is a circuit for comparing the amplitude of analog signals. The electrical energy store can be used to generate a reference voltage for the comparator, which is a first input of the Comparator is supplied. For this purpose, between the first input of the comparator and the electrical energy storage z. B. a voltage divider with a series resistor and a reverse-biased Z-diode arranged. The second input of the comparator, the rectified output voltage of the piezoelectric element is supplied.

The metering device can, for. B. be realized as in a clock. The energy reservoir is preferably coupled to a pivoting element (eg armature, balance shaft). The mechanical energy can be converted into the kinetic energy of the pivoting movements of the pivoting element. The pivoting element can, for example, drive a shaft by means of a gear or escape wheel and cause this shaft to rotate. The shaft preferably belongs to the transport device or is mechanically coupled to the transport device. The swing frequency of the swing member may be controlled by the feedback circuit. Thus, the rotational frequency of the shaft and consequently the predetermined speed of the activator can be adjusted.

In one variant, the dosing device may comprise a spring coupled to a balance shaft, which may be wound up by, inter alia, spontaneous mechanical action. The swing frequency of the balance wheel can be adjusted by the length of the spring. The length of the spring can be adjusted by means of a clamping element fixed to a movable, z. B. electromechanically or electromagnetically controllable element is connected, which can preferably perform a linear movement. It is advantageous if the mechanical parameters of the metering device are chosen such that the initial frequency or speed of the excitation device is in the vicinity of the intended operating point. Preferably, the initial frequency of the excitation device is selected below the operating point. The feedback circuit ensures that the frequency of the excitation device is increased during the start-up phase. In normal operation, this frequency is held by the feedback near the operating point.

The control of the frequency of the metering device can be accomplished in an advantageous manner by means of a comparator which is electrically coupled to the electromechanically or electromagnetically controllable element. The comparator compares the voltage generated at the piezoelectric element with a reference voltage and gives z. B. when exceeding the predetermined voltage level, a negative and falling below this level, a positive control voltage. The electromechanically or electromagnetically controllable element is dependent on the state of the comparator, d. H. moved according to the sign of the control voltage in one direction or in the opposite direction to it. The position of the controllable element determines the mechanical parameters and thus the frequency of the metering device.

The piezoelectric generator can be a z. B. to the electrical energy storage device or to another electrical energy storage electrically coupled starter device (switch), which is provided for triggering the excitation device by means of an electrical pulse. In this case, the stored electrical charge is supplied to the feedback circuit, which boosts the excitation device. The Piezo However, generator can also include a starting device for triggering the excitation device by means of a mechanical action on this device. The starting device can, for. B. be operated manually. In addition, a switch for interrupting the excitation device may be provided.

Instead of just one resonance system, the generator may comprise a plurality of resonance systems, which are preferably excited at the same frequency but with different phases.

The piezoelectric generator will now be explained with reference to schematic and not to scale figures. They show schematically:

Figure 1 shows a basic structure of a piezoelectric generator with a feedback circuit;

Figure 2 shows a basic structure of a piezoelectric generator with an energy storage device;

FIG. 3 shows an exemplary implementation of the piezoelectric generator according to FIG. 2 for the embodiment with a plurality of electromechanical transducers connected in parallel;

FIG. 4 shows the time dependence of the voltage generated by the parallel-connected electromechanical converter according to FIG. 3;

FIG. 5 shows a further exemplary implementation of the piezoelectric generator according to FIG. 2 for the embodiment with a plurality of electromechanical converters connected in parallel;

6 shows a detail of the piezator with a Rectifier in the form of a diode bridge;

FIG. 7 shows an embodiment of the piezoelectric generator according to FIG. 2 with a plurality of electromechanical transducers connected in parallel, wherein a separate activator is provided for each transducer;

Figure 8 in cross section the piezoelectric generator with a vibrating device and biased piezoelectric element, wherein vibrating elements of the vibrating device are deflected by an activator (top) and swing freely (bottom);

Figures 9, 10 is a perspective view of a transport device which sets the activator in motion;

Figure 11 is a plan view of a transport device in which a plurality of activators are mounted on a rotating device in the form of a disc;

Figure 12 is a plan view of a transport device in which two activators are mounted on a spinner in the form of a spoke at both ends of the spoke;

FIG. 13 shows an oscillating device which can be excited by the air pressure and has a reservoir for the compressed air;

FIG. 14A shows a detail of the air reservoir according to FIG. 13 with a valve in the form of a flap which is fastened to the air reservoir at one end;

FIG. 14B shows a detail of the air reservoir according to FIG. 13 with a valve in the form of a membrane; FIG. 15A shows the view of an inlet opening of the air reservoir according to FIG. 13 with a valve in the form of a small plate, which is rotatable about its center axis, with the inlet opening closed;

FIG. 15B shows the view of an inlet opening of the air reservoir according to FIG. 13 with a valve in the form of a plate, which is rotatable about its central axis, with the inlet opening open;

FIG. 16 shows an exemplary realization of the feedback circuit;

FIG. 17 Dependence of the voltage generated by the generator on the excitation frequency.

FIG. 1 shows schematically the construction of a piezoresistor 1 with a mechanical resonance system 5, which comprises an oscillating device 51 and a piezoelectric transducer 2 (piezoelectric element). The resonance system 5 has a resonance frequency f _R.

The oscillating device 51 and the piezoelectric element 2 are mechanically coupled together. The mechanical coupling between the oscillating device 51 and the piezoelectric transducer 2 is indicated by the double arrow 43. Thanks to this coupling, the transmission of mechanical energy to the piezoelectric transducer is possible.

The oscillating device 51 can be excited by means of an activator 6 to vibrate. The oscillation frequency preferably agrees with the resonance frequency f _{R of} the resonance system. The activator 6 is a moving part which nergie an external mechanical force 7 receives and doses this, ie with an excitation frequency f _a on the vibrating device 51 transmits and thus brings this device to vibrate. Preferably, f _a = f _R / n, where n is an integer between 1 and 5.

FIG. 2 shows a variant of the piezoelectric generator 1, which comprises an energy store 71, in which the mechanical energy generated by the external mechanical force 7 is stored. The energy store 71 is coupled to the activator 6 or to a transport device for transporting the activator, which is indicated by the arrow 41 in FIG.

The activator 6 can be used for the deflection of vibratable elements of the oscillating device 51. In this case, a mechanical contact 42 can exist between the activator 6 and the oscillating device 51 in predetermined time slots. The z. B. as a valve to release the pressed air from the energy storage 71 designed activator 6 can also stimulate the vibrating device 51 without contact by - as indicated in Figure 13 by the arrow 68 - generated in predetermined time slots an air jet in the direction of the main surfaces of the oscillatory elements becomes.

In a variant, the energy of the translational or rotational movement of the activator 6 is converted into oscillations of the oscillating device 51. The oscillating device 51 transmits a variable compressive stress to the piezoelectric element during oscillation. The piezo element is electrically connected to an electrical load 3 - consumer. In the piezo element, the transformation of the mechanical energy into the electrical, which is supplied to the electrical load 3 takes place. In principle, the piezoelectric element may have any structure.

The piezoelectric transducer 2 is preferably coupled electrically by means of a feedback loop to the activator 6 or to a transport device for transporting the activator 6 explained in conjunction with FIGS. 9 to 12. A portion of the voltage generated in the piezoelectric element is conducted into the feedback loop in which a feedback circuit 26 is arranged.

An alternating voltage is generated at the piezo element. The piezo-generator 1 may be provided for generating an AC voltage. The piezoelectric generator 1 can also be used to generate both a DC voltage. To generate the DC voltage from the AC voltage, a rectifier 31 is provided. To generate the DC voltage several branches can be connected in parallel, each with its own resonance system, wherein in the various branches, the AC voltage is generated with different phases.

The signal generated at the piezoelectric element is rectified by means of the rectifier 31 and preferably stored on the electrical storage element 32. As a rectifier 31 z. B. a diode circuit with at least one diode suitable. As electrical storage element 32, in particular a circuit is suitable which comprises at least one capacitor or accumulator. The stored at the memory element 32 e- lectric energy can be consumed by the load 3.

Part of the generated signal is used for feedback. At the output of the feedback circuit 26, a control signal for controlling a metering device 27 is generated. The metering device 27 comprises a mechanism whose frequency or speed can be adjusted by the control signal of the feedback circuit 26. This mechanism is mechanically coupled to a transport device to which the activator 6 is attached, see Figures 9 and 10. The mechanical parameters of the metering device 27 can be changed so that the operating point corresponding excitation frequency f _a can be adjusted.

The feedback signal for the feedback circuit 26 can be tapped at the output of the rectifier 31 in all variants shown as in FIG. The feedback signal may alternatively, as in Figure 2 between the piezoelectric transformer 2 and the rectifier 3, d. H. at the input of the rectifier, are tapped.

FIG. 3 shows an exemplary piezoelectric generator comprising a number N of branches connected in parallel, wherein a resonance system 5-1, 5-2... 5-N is arranged in each branch, and where N> 1. In the ith branch is a piezoelectric element 2-i and a rectifier 31-i arranged, i is the atomic number of the branch, i = 1, 2 ... N. All branches are preferably connected to a common energy storage 32 for electrical energy (here capacitor).

Each piezoelectric element 2-i is mechanically coupled to a vibrating device 51-i. In at least one branch - preferably at the output of the rectifier 31-i - a feedback circuit 26 is connected. This is the first (upper) branch in FIG.

For at least one branch, a feedback circuit 26 is preferably present at the output of the rectifier 31-i. concluded. The tap of the feedback signal for the feedback circuit may alternatively be carried out before the rectifier circuit as in the variant according to FIG. In the latter case, the conductive connection 312 is replaced by a conductive connection 311, which is indicated in Figure 3 by a dashed line.

To excite the resonance system of the respective branch, an activator 6-1, 6-2 ... 6-N is provided. Each activator is preferably mechanically coupled to a common energy storage 71, which is indicated by arrows 41-1, 41-2 and 41-N. By means of the feedback circuit 26, the activators 6-1, 6-2 ... 6-N are respectively controlled in such a way that in each generator branch the excitations 42-1, 42-2 ... 42-N and the resonance system 5-1, 5-2 ... 5 -N are synchronized with each other.

The resonance systems of the various branches are preferably formed substantially the same and are driven at the same frequency but with different phases. FIG. 4 shows the time profile of the voltage U generated by the parallel-connected electromechanical converter according to FIG. The voltage Ui, U ₂ , etc. is generated by the piezo elements 2-1, 2-2 and so on. The phases of the voltages U ₁ , U ₂ are shifted from each other. This makes it possible to smooth the amplitude fluctuation (pulsation) of the output voltage of the generator.

FIG. 5 shows a further exemplary embodiment of the piezoelectric generator with a plurality of parallel-connected piezoelectric elements 2-1, 2-2... 2-N. Each rectifier 31-1, 31-2 ... 31-N may comprise, as in FIG. 5, a diode in the series branch and a diode in the shunt branch. Here, by means of the feedback circuit 26, a transport device 6 'is actuated, to which the activators 6-1, 6-2 ... 6-N are coupled. The tracks of the activators are preferably parallel to each other. For this purpose, a transport device explained in conjunction with FIGS. 9 and 10 with a conveyor belt is particularly well suited. Various activators are spatially offset from one another in FIGS. 9, 10, preferably in the y-direction. However, it is also possible to arrange different oscillation devices following one another in the y-direction along the track of an activator 6 and thus to excite different oscillating devices with different phases but with the same activator 6.

FIG. 6 is a detail of a piezoelectric generator with a rectifier 31 or 31-1, 31-2... 31-N in the form of a diode bridge. The input of the diode bridge is connected to the piezoelectric element 2 and its output to the electrical energy storage 32 and / or the load 3.

FIG. 7 shows an embodiment of the piezoelectric generator with a plurality of piezoelements connected in parallel, wherein a separate activator is provided for the excitation of each resonance system. To the piezoelectric element with the atomic number i = l, 2 ... N is a separate feedback circuit 26-1, 26-2 ... 26-N connected to synchronize the respective activator 6-1, 6-2 ... 6-N and the resonance system to be excited thereby. Otherwise, the mode of operation of the arrangement shown in FIG. 7 is explained in conjunction with FIG.

FIG. 8 shows an exemplary implementation of the piezoelectric generator with a vibrating device which has the shape of a tuning fork, that is to say it is designed as a U-piece. The U-piece has two legs and a connector that connects the two legs together. The legs of the U-piece are vibrating elements 8a, 8b, which represent the wings of the vibrating device. The vibrations of the second vibrating element 8b are correlated with the vibrations of the first vibrating element 8a.

The connecting piece of the U-piece has a mounting portion 17 in which the oscillating device on a support, not shown, such. B. is attached to the housing of the generator.

The piezoelectric element 2 is clamped in the initial state between the wings (legs) of the vibrating device in the vicinity of the connecting piece and thereby biased. In a variant, the piezoelectric element 2 is held exclusively by the legs of the oscillating device. But it is also possible that the wings are mainly used for periodic compression of the piezoelectric element 2, wherein the piezoelectric element is additionally supported, held or carried by a mechanically decoupled from the vibrating device holding device.

The legs of the oscillating device, for example, strip-shaped bending springs. The oscillating device also includes weights 9a, 9b, which are mounted at the free end of the respective vibrating element 8a, 8b and suitable for storing a mechanical energy.

The weights 9a, 9b in the contact region and the activator 6 preferably have oblique, mutually facing surfaces which abruptly stop at a position which is touched last when the activator slides out of the contact region. At this point, the maximum deflection of the Scoring elements 8a, 8b achieved. The sloping surfaces preferably each intersect with a horizontally oriented surface. Advantageously, in this case, when the activator 6 passes through the contact region of the oscillating device, an abrupt release of these oscillating elements is effected immediately after reaching the maximum deflection of the oscillating elements 8a, 8b. This makes it possible to transfer the mechanical energy to the vibrating device most efficiently.

The activator 6 may be formed in particular in the form of a wedge. The activator 6 moves in the figure 8 from left to right between the weights 9a, 9b and thereby slides on the facing him surfaces of these weights. As soon as the cross-sectional size of the activator exceeds the minimum distance between the weights 9a, 9b, the weights 9a, 9b are pressed apart, which is indicated in the figure 8 above with arrows.

The weights 9a, 9b are chamfered on the mutually facing sides such that the sliding of the wedge between these weights is facilitated. Due to the wedge shape of the activator 6 and the chamfering of the weights 9a, 9b, it is possible to press apart the vibrating elements 8a, 8b particularly efficiently and without jerking. The activator 6 can also move perpendicular to the cross-sectional plane shown in FIG. 8, wherein the slope of the weights 9a, 9b preferably always runs along the direction of movement of the activator 6.

In the case of the deflection of the oscillating elements 8a, 8b caused by the movement of the activator, an energy is stored in them. As soon as the activator leaves the contact area of the oscillating device, the weights start to ter the effect of a restoring force to move in a reverse direction. The direction of movement of the oscillating elements 8a, 8b immediately after the activator has slid out of the contact region is indicated in the figure 8 below with arrows. In this case, the energy stored in the weights 9a, 9b is converted into the oscillatory energy of these weights or into the oscillation energy of the oscillating device, since the movement of the weights 9a, 9b causes the oscillating elements 8a, 8b to oscillate.

During the oscillation period of the oscillating elements 8a, 8b, piezoelectric element 2 undergoes a periodically changing mechanical compressive stress in the vertical direction z, which leads to the contraction of the piezoelectric element. The compressive stress generated on the piezoelectric element 2 is converted into an electrical energy z. B. implemented as explained below. At the electrodes 10a, 10b, 10c of the piezoelectric element 2 occurs due to the piezoelectric effect, an electrical charge which is supplied to the electrical load 3 or the energy storage. The front-side electrodes 10a and 10b are both connected to a first and the middle electrode 10c of the piezoelectric element to a second electrode of the load 3, so that the electric charge can flow from the piezoelectric element 2.

The dependence of the alternating voltage U on the piezoelectric element 2 on the time t is shown schematically in FIG. This voltage is proportional to the amplitude of the mechanical vibrations of the vibrating elements 8a, 8b. This amplitude decreases with time as the vibrations are damped by friction losses and energy dissipation. The vibrating elements 8a, 8b oscillate against each other, preferably in antiphase, but with the same amplitude. The portion of the connector located near the symmetry axis of the vibrator remains substantially immobile in the vibration of the vibrating members 8a, 8b. The fastening region 17 is preferably arranged in this region of the connecting piece. Thus, the vibrations of the vibrating elements 8a, 8b are attenuated only slightly by the connection with the carrier.

The piezoelectric element 2 shown in FIG. 8 represents a multilayer component or a piezostack, i. H. a stack of alternately arranged piezoelectric layers and metal layers. Each metal layer is formed into an inner electrode. The first internal electrodes (not shown in FIG. 8) are connected to a first external electrode 10a, the second internal electrodes are connected to a second external electrode 10b and the third internal electrodes are connected to a third external electrode 10c. The outer electrodes 10 a, 10 b, 10 c are arranged on the surface of the piezoelectric element 2.

FIGS. 9 and 10 show a mechanical arrangement for exciting the oscillating device 51, in which, unlike the variant shown in FIG. 8, the activator not shown here does not extend along the longitudinal direction x of the oscillating elements 8a, 8b another lateral direction y, ie transverse to it. The weights 9a, 9b are bevelled so that the distance between them in the direction y is smaller.

The oscillation frequency of the oscillating device 51 can be adjusted by the mass of the weights 9a, 9b, the length of the oscillating elements 8a, 8b and the position of the piezoelectric element 2. The Oscillation frequency is preferably equal to the resonant frequency of the piezoelectric element. 2

The excitation of the oscillating device 51 by the activator 6 may be periodic, wherein the period of the excitation is preferably equal to the oscillation period of the oscillating device 51 or an integer multiple of this period. The period of the excitation can be reduced if necessary thereby and thus the excitation frequency can be increased, that instead of only one activator 6 such. B. in the variants of Figures 11 and 12, a plurality of preferably similar activators 6, 6a, 6b, 6c are used, wherein the successive activators are arranged at the same distance from each other on a transport device. The transport device may, as in FIGS. 9 and 10, comprise a conveyor belt or, as in FIGS. 11 and 12, a rotary device.

In FIGS. 9, 10, a transport device is presented which controls the activator 6 in the direction y, d. H. from left to right, linear offset. The transport device comprises a conveyor belt 61 to which the activator 6 is attached. On this band also another activator 6a is attached.

The transport rollers 62a, 62b each rotate clockwise about an axis of rotation and thus cause the movement of the conveyor belt 61 also in a clockwise direction. The conveyor belt 61 has, in the variant according to FIG. 9, a laterally protruding tongue 63, to which the wedge-shaped activator 6 is fastened. The tongue 63 protrudes in a direction which is transverse to the direction of movement of the conveyor belt 61 or activator 6. When the activator passes the contact region of the oscillating device, the deflection of the weights 9a, 9b already explained in connection with FIG. 8 is effected. In FIG. 10, the lower part of the conveyor belt 61 is arranged between the oscillating elements 8a, 8b. The activator 6 is here - in contrast to the variant according to FIG. 9 - arranged in the central region of the conveyor belt 61. In order that the inwardly directed part of the activator 6 can also pass unhindered in the area of the transport rollers, the transport rollers 62a, 62b each have a region 64 with a smaller cross section than its intended areas for belt transport. The career of the activator 6 passes between the weights 9a, 9b.

The oscillating device 51 shown in FIGS. 9 and 10 is also shown in a side view in FIG.

The activator may, as in the variants according to FIGS. 11 and 12, be mounted on a turning device instead of a running belt. Several activators can be mounted on the rotating device, whereby the excitation frequency can be increased with the same rotational frequency of the rotating device compared to the variant with only one activator. The arrangement of the rotating device and the activators is preferably point-symmetrical with respect to their center lying at the axis of rotation.

In Figure 11, the rotating device is realized as a disk 16c rotating about an axis perpendicular to the main planes of the disk. Alternatively, as in the variant according to FIG. 12, the rotating device may have at least one web 16a, which extends perpendicular to the axis of rotation and is rotatable about the axis of rotation. Through the center of the web 16a, the axis of rotation goes through. At both ends of the web 16a an activator is attached in each case. In any case, a portion of the raceway of each activator 6, 6a, 6b, 6c extends between the vibrating elements 8a, 8b.

Fig. 13 shows an air pressure excitable vibrating device 51 and a compressed air storage 71. The reservoir 71 comprises a reservoir 60 with an air inlet opening 65 which can be closed by a valve 66 and an air outlet opening 69 which can be closed by the activator 6.

The air can be pumped into the container 60, in which the valve is open. The valve 66 is only opened when an air pressure in the direction from the outside to the inside arises in the region of the inlet opening 65. The escape of the air from the container 60 through the inlet opening 65 is prevented by the valve 66.

In designated first periods of time, the outlet opening 69 is opened by the activator 6. The emergence of the air through the outlet opening 69 is prevented in the second periods by the activator 6. The activator 6 represents a valve which is controllable by means of the feedback loop shown in FIGS. 1 to 3, 5 and 7.

Various examples of valves 6 or 66 are shown in Figs. 14A, 14B and 15A, 15B. FIG. 14A shows a detail of the air reservoir according to FIG. 13 with the valve 66 in the form of a flap 66a, which is fastened to the air reservoir at one end. FIG. 14B shows the valve in the form of a membrane 66b. Figures 15A and 15B show the view of an inlet opening of the air tank 60 with a valve in the form of a small plate 66c, which is rotatable about its central axis DD, with closed (Fig. 15A) and open (15B) inlet opening. In FIG. 15A, the plane of the chip 66c is arranged transversely and, in FIG. 15B, parallel to the normal of the opening 65.

Figure 16 shows an exemplary embodiment of the feedback circuit. The feedback circuit 26 comprises a comparator 261. A reference voltage U _{ref is} applied to the non-inverting input of the comparator. The reference voltage is supplied by the electric storage element 32 and stabilized by the Zener diode 262. The reference voltage determines the operating point of the resonance system. At the inverting input of the comparator 261, the voltage U taken off at the output of the rectifier 31 is applied.

The supply voltage of the comparator is supplied by the electric storage element 32 and stabilized by means of the Zener diode 263.

The output signal of the comparator 261 is used to control the metering device 27. The output of the comparator can z. B. can be used for switching an electromechanical element with which the mechanical properties of the metering device are adjustable.

The comparator may include a built-in amplifier. The output signal of the comparator can also be amplified by a separate amplifier, not shown in FIG become .

FIG. 17 shows the dependence of the voltage U on the excitation frequency f _a . This voltage measured at the input of the comparator is proportional to the voltage generated at the output of the rectifier. f _a , ₀ is the initial value of the excitation frequency and f _a , i is the excitation frequency corresponding to the operating point. The frequency f _a , ₀ is determined by the mechanical parameters of the metering device 27 in the idle state.

f _a , _R is the excitation frequency which is equal to an integer multiple of the resonance frequency. In this example, the frequency f _a , ₀ and the operating point below the frequency f _a , R has been chosen at which the maximum voltage can be generated. During the transient phase, the parameters of the dosing device 27 are changed such that the excitation frequency is increased up to the value f _a , i at which the voltage level U _ref given at the second input of the comparator is reached. When this level is exceeded, the excitation frequency is lowered by the switching of the comparator and again increased when repeatedly falling below this level, so that the excitation frequency is stabilized in the vicinity of the operating point. The slight change in frequency near the operating point is indicated by a double arrow 28 in FIG.

The resonance system is not limited to the embodiments shown. Any configurations of the piezoelement and the oscillating device are possible. LIST OF REFERENCE NUMBERS

1 piezoelectric generator

2 piezo element

26 feedback circuit 261 comparator

262, 263 Z-diodes

27 dosing device

3 electrical load

31 rectifier

311, 312 conductive connection

32 electrical storage element 41, 43 mechanical coupling

42 mechanical stimulation

5 resonance system (electromechanical transducer)

51 oscillating device

6, 6a, 6b, 6c activator

60 containers for the pressed air

61 conveyor belt

62a, 62b transport rollers

65 air intake opening

66 valve

68 air jet

69 air outlet opening

7 external mechanical force

71 storage for mechanical energy

8a, 8b oscillating elements

9a, 9b weights

10 a, 10 b, 10 c outer electrodes of the piezoelectric element 2

11 piezoelectric layer

12 internal electrodes 15a, 15b connecting wire 16 ring 17 mounting area

AA rotary axis

U voltage after the rectifier

U _ref reference voltage

Ui generated in the first electromechanical transducer

Voltage U _N generated in the Nth electromechanical transducer

Voltage f _a excitation frequency f _a , o initial value of the excitation frequency f _a, i the excitation frequency f _a , _R corresponding to the operating point excitation frequency, which is equal to an integer

Multiples of the resonance frequency is f _R resonance frequency t time x first lateral direction, which coincides with the longitudinal direction of

Oscillating elements 8a, 8b match y second lateral direction z vertical direction

Claims

claims

1. Piezo generator

with a resonance system which can be excited to mechanical vibrations and which comprises a piezoelectric transducer (2),

with a feedback circuit (26) electrically connected to the piezoelectric transducer (2), and

- With a device for exciting the resonance system, which is controllable by the feedback circuit (26).

2. Piezoelectric generator according to claim 1,

- wherein the resonance system has a natural frequency,

- Wherein the device for exciting the resonance system for adjusting the frequency of the mechanical vibrations at the natural frequency of the resonance system is suitable.

3. Piezoelectric generator according to claim 1 or 2,

with at least one activator (6) for exciting the vibrations of the resonance system,

- Wherein the feedback circuit (26) is provided for controlling the frequency of action of the activator (6) on the resonance system.

4. Piezoelectric generator according to claim 3, which comprises an energy store (71) for mechanical energy in the form of a spring, which is mechanically coupled to the activator (6).

5. Piezoelectric generator according to claim 3,

comprising an energy store (71) for mechanical energy in the form of a pressed air,

- wherein the activator (6) is designed as a valve which is suitable for releasing the pressed air, - When the valve is open, an air pressure is generated on vibratable parts of the resonance system.

6. Piezoelectric generator according to one of claims 3 to 5,

with a transport device to which the activator (6) is attached,

- Wherein the feedback circuit (26) is provided for setting a predetermined speed of the transport device.

7. Piezoelectric generator according to one of claims 1 to 6, wherein the resonance system comprises an oscillating device (51) comprising mutually oscillatable oscillating elements (8a, 8b), between which the piezoelectric transducer (2) is clamped.

8. Piezoelectric generator according to claim 3 and 7, wherein the activator (6) for changing the distance between the vibrating elements (8a, 8b) is suitable.

9. Piezoelectric generator according to claim 7 or 8, wherein the oscillating elements (8a, 8b) in the region of their freely oscillatable ends each have a weight (9a, 9b).

10. Piezoelectric generator according to claim 7, wherein the oscillating elements (8a, 8b) are magnetizable, so that they are electromagnetically deflectable by the feedback circuit (26).

11. Piezoelectric generator according to claim 3, wherein the feedback circuit (26) is suitable for generating control pulses, with which the activator (6) is driven.

12. Piezoelectric generator according to one of claims 1 to 11, wherein the feedback circuit (26) comprises an amplifier.

13. Piezoelectric generator according to one of claims 1 to 12, with an electrical energy store (32) for storing the electrical energy generated at the piezoelectric transducer (2).

14. Piezoelectric generator according to claim 13, wherein the electrical energy store (32) for supplying energy to the feedback circuit (26) is provided.

15. Piezoelectric generator according to claim 13 or 14,

- wherein the feedback circuit (26) comprises a comparator,

- wherein the electrical energy store (32) is used to generate a reference voltage for the comparator.

16. Piezoelectric generator according to one of claims 1 to 15, with a rectifier (31) which is electrically connected to the piezoelectric transducer (2).