DE10136628A1 - Method for operation of an ultrasonic transducer for transmission and receipt of ultrasound waves whereby damping of initial membrane vibration is improved so reducing interference and increasing measurement accuracy - Google Patents

Abstract

Method wherein a membrane is first excited to transmit the waves, then damped and then caused to vibrate by the returning reflected waves. To damp the excitation of the membrane, the membrane vibrations are measured and then the membrane is vibrated in a phase-displaced manner to cancel out the initial excitation vibrations. Measurement of membrane vibrations and creation of damping membrane excitation are carried out sequentially, i.e. in a time-displaced manner. The invention also relates to a corresponding control device for an ultrasonic transducer and use of the inventive transducer in a motor vehicle parking system.

Description

The present invention relates to a method of operation an ultrasonic transducer for sending and receiving Ultrasonic waves using a membrane. To send out Ultrasonic waves are used for a predefinable membrane Time excited. After emitting ultrasonic waves the membrane vibrations are damped. As part of the Attenuation, the membrane vibrations are recorded, and the Membrane is in phase, but with opposite Amplitude excited to the detected vibrations. To receive The membrane vibrations are detected by ultrasonic waves.

The present invention also relates to a Ultrasonic transducer for sending and receiving Ultrasonic waves using a membrane. The Ultrasonic transducer has a membrane, means for emitting of ultrasonic waves by exciting the membrane for one predefinable duration, means for the subsequent steaming of the Membrane vibrations and means for receiving Ultrasonic waves by detecting the membrane vibrations. The damping of the membrane vibrations takes place by detecting the Membrane vibrations and actuation of the membrane in phase, but with the opposite amplitude to the detected Vibrations.

Finally, the invention also relates to a control device for such an ultrasonic transducer.

Ultrasonic transducers are known from the prior art, at which a sound-transmitting membrane also for receiving reflected sound waves is used. such Ultrasonic transducers are used, for example, in the motor vehicle sector Devices for measuring the distance of a motor vehicle an object (so-called parking systems). It will be from the running time of a signal from sending to receiving the the distance of the signal reflected from an object Motor vehicle determined to the object.

The well-known ultrasonic transducer is in a cup-shaped Housing made of metal, the membrane as one Metal membrane is made of aluminum, for example. On the Inside the membrane is a disk-shaped piezo element attached, which is provided with two connecting electrodes. The Electrodes are contacted, for example, by two copper strands, which are each soldered to a connection electrode. The The second electrode is either contacted directly on the second electrode or indirectly via the metallic one Pot. The electrode side facing the pot leads mass, and there is a between this electrode and the pot low-resistance contact. The earthed pot offers one effective protection against spark discharge (electrostatic discharge, ESD) in the range of about 25 kV and before the coupling electric fields.

Ultrasonic transducers of the type mentioned, in which the sounding membrane also for the reception of reflected Sound waves are used alternately as transmitters and operated as a receiver. For sending ultrasound The piezo element is emitted with an excitation voltage Excited range of some 10 volts, causing the membrane of the Ultrasonic transducer set in high-frequency vibrations and consequently emits ultrasonic waves. After a Predefinable transmission time is the excitation of the piezo element ended and the ultrasonic transducer in the receiving mode switched. Reflected sound waves offset the Membrane vibrates, which separates between the Connection elements of the piezo element have a received voltage in the Forms a range of some 100 microvolts from one Evaluation unit is recorded, strengthened and evaluated.

This is a problem with the known ultrasonic transducers After-emission behavior of the membrane after transmission of ultrasonic waves. Because the excitation voltage is essential ringing is greater than the received voltage the membrane to a strong adulteration of the Reception voltage. For this reason, the Membrane vibrations following the emission of Ultrasonic waves are damped so far that they become clear are below the vibrations reflected by Sound waves are caused.

Various measures are known from the prior art Reduction of the reverberation behavior of the membrane is known. On the one hand, after the excitation of the piezo element has ended a predeterminable decay period can be waited for before the Ultrasonic transducer is switched to receive mode. During this decay period, the amplitudes of the from the excitation of the membrane caused vibrations so far have subsided that they are significantly less than that of the are reflected vibrations caused vibrations and as far as possible avoid interference in the received voltage becomes.

To reduce the cooldown, it is further known to mechanically and / or electrically the membrane dampen. Foam is used for mechanical damping or a similar damping material inside the pot introduced on the membrane. However, the membrane cannot be damped as much as desired, because an increase in mechanical damping of the membrane to a reduced Receive voltage and thus to a lower sensitivity of the ultrasonic transducer.

Electrical damping is achieved by connecting one in parallel Inductance (e.g. a secondary coil of a transformer) and achieved resistance. The equivalent circuit diagram of the Diaphragm corresponds to a series resonant circuit. Through the Inductance is the parallel capacitance in the Equivalent circuit composed and the resonant circuit by the Resistance deprived of energy, resulting in a damping of the Leads to membrane vibrations. To do this, the resonance frequency of the formed parallel resonant circuit can be selected accordingly. The coil required for this (inductance) does that However, ultrasonic transducers are sensitive to magnetic Interference.

Furthermore, it is known from the prior art that Membrane in a feedback circuit for active Integrate vibration damping. However, none of the two connection electrodes of the piezo element are connected to ground become. So the pot is not connected to earth and its protective function against ESD and EMC (electromagnetic Compatibility) is no longer given.

Furthermore, it is known to flow through a Series resonant circuit, the equivalent circuit of the membrane corresponds to measuring via a current shunt (measuring resistor) and the membrane capacitance through a bridge circuit compensate. With the measured current, the vibration of the Membrane active and counter-clockwise and this thereby be dampened. As part of the countermeasures Piezo element so excited that it is in the membrane Vibrations offset the detected vibrations are opposed. However, neither can Piezo electrodes are connected to ground with low resistance. Consequently the pot cannot be connected directly to earth and its protective function against ESD no longer exists. An EMC Protection with a low-impedance connection is only included given reduced effect.

Finally, it is known the deflection or the Movement speed of the membrane by an additional Measure the contact of the piezo electrode. With this signal can the membrane vibrates actively and in phase counteracted and thereby dampened. By the additional contact on the electrode increases the Manufacturing and material costs (possibly additional sensitive amplifier necessary) and especially the Requirements for the quality of the connections with regard to the exposure to mechanical vibrations and the Sensitivity to mechanical resonances.

A correct countermeasure that tries this to avoid additional third contact by the two existing contacts are used, is hardly feasible, since such circuits tend to oscillate. This arise because the signals for correct phase countermeasures distort the measurement of the membrane vibrations and thus the Correct position of the countermeasures not observed can be. This out of phase situation leads to Rule to oscillations, the reception of Make ultrasonic signals impossible.

The present invention is based on the object an ultrasonic transducer to reduce the susceptibility to faults, the converter being as sensitive as possible should have a short decay of the membrane after Arousal should be ensured and at the same time the Circuit should be protected against ESD.

To solve this problem, based on the method of initially suggested that the detection of the Membrane vibrations and the excitation of the membrane under the Damping is carried out at different times.

According to the invention is used to dampen the membrane vibrations an active damping is used, in which the membrane such is excited that it is caused to vibrate, although in phase with the membrane vibrations to be damped but with inverted amplitude are formed. The damping takes place by counteracting the membrane vibrations as part of a Regulation, which ensures a particularly short decay time Membrane following the emission of ultrasonic waves is ensured. This is the state of the art method of continuous countermeasures used, d. H. the simultaneous detection of those to be damped Membrane vibrations and countermeasures, abandoned. In the present invention, the detection of Rather, membrane vibrations and excitation of the membrane staggered in time. This has the advantage that the Danger of oscillations through a suitable control of the Ultrasonic transducer significantly reduced and even eliminated can be.

According to an advantageous development of the present Invention is proposed that for detecting the Membrane vibrations as part of the damping one of the Current or voltage signal dependent on membrane vibrations generated and in a receiving circuit of the ultrasonic transducer is recorded. That vibration-dependent current or Voltage signal can, for example, by a on the membrane attached piezo element are generated. It can, for example, that of the piezo element depending on the membrane vibrations voltage built up between two connection electrodes measured become.

Instead of a voltage measurement, a current measurement can also be used be carried out, the membrane then in one short-circuited state is operated. Therefore, according to proposed a preferred embodiment of the invention, that the membrane is operated in short-circuit mode and for Detect the membrane vibrations as part of the damping Current signal is detected. The membrane or the piezo element is operated short-circuited when received, and a current measurement is carried out via a current shunt. Due to the short-circuit operation, the damping through Capacity of the membrane eliminated, resulting in a higher Sensitivity of the ultrasound transducer on reception leads because the reception power is optimally used. Furthermore the short-circuit operation of the membrane enables direct Measurement of the current through the series circuit (equivalent circuit diagram membrane) without additional contact (Connection electrode) on the piezo element. This results in lower manufacturing and manufacturing costs for the Ultrasonic transducers.

According to another advantageous development of the present invention it is proposed that a current or voltage signal to excite the membrane using a Operational amplifier from a lower Supply voltage is generated. When using a Piezo element to excite the membrane Ultrasonic transducer in a parking system Motor vehicle is used is an excitation voltage from a few 10 volts, in particular 80 to 100 volts, required. The operational amplifier must therefore be out of the Supply voltage of e.g. B. 12, 24 or 42 volts generate the required excitation voltage. Because of the engagement an operational amplifier can be connected to a transformer Generation of the excitation voltage can be dispensed with. Since the Coils of a transformer, especially the secondary coil, the receiving circuit of the ultrasonic transducer with disturbing Act on signals and thus falsify the Receive voltage if it has a magnetic interference field (e.g. from an electric motor of a cooler Motor vehicle) are exposed, the circuit of the Ultrasonic transducer when using an operational amplifier and insensitive to the absence of the transformer magnetic interference fields. The operational amplifier can be in one Control unit or arranged directly in the ultrasonic transducer his.

Alternatively, it is proposed that a current or Voltage signal to excite the membrane using a Transformer from a lower supply voltage is generated, with a secondary coil of the transformer from decoupled from a receiving circuit of the ultrasonic transducer becomes. The circuit is due to the proposed decoupling of the ultrasonic transducer insensitive to magnetic Interference.

The secondary coil of the transformer is advantageously from the receiving circuit of the ultrasonic transducer through a antiparallel diode pair decoupled. Because diodes are one Have reverse voltage of about 0.6 volts and induced Usually, voltages due to magnetic interference fields are less than 0.6 volts, the circuit of the Ultrasonic transducer by decoupling using a antiparallel diode pairs insensitive to magnetic Interference. Higher voltages, for example the excitation voltage, the diodes can easily pass through.

As a further solution to the object of the present invention starting from the ultrasound transducer mentioned kind suggested that capturing the Membrane vibrations and the excitation of the membrane under the Damping can be carried out at different times.

According to an advantageous development of the present Invention is proposed that the ultrasonic transducer Means for performing the method according to the invention having.

It also becomes a particularly advantageous use of the ultrasonic transducer according to the invention in one Parking system for a motor vehicle proposed. This is where the main advantages of the Ultrasonic transducer according to the invention, namely a high Reception sensitivity and low susceptibility against magnetic interference fields, for carrying. With the Ultrasonic transducer according to the invention, the distance of a Motor vehicle to an object particularly precisely, reliably and can be determined up to very short intervals.

As yet another solution to the problem of the present Invention is based on the control unit of the beginning mentioned type suggested that the control device the means for detecting the membrane vibrations and the means for Excitation of the membrane at different times as part of the damping controls each other. The control unit includes a fixed wired logic or a computing device, preferably one Microprocessor on which a control program can run, that on a memory element, preferably on a flash Memory that is stored. To process the Control program on the microprocessor becomes the program either as a whole or in sections from the Memory element read out and sent to the microprocessor transfer. In the control program u. a. the inventive method, namely the alternating Control of the means for detecting the membrane vibrations and the means for countermeasures.

Other features, applications and advantages of Invention result from the following description of Embodiments of the invention shown in the drawing are shown. Thereby form all described or shown features alone or in any combination the subject of the invention, regardless of its Summary in the claims or their Relationship and regardless of their wording or Representation in the description or in the drawing. It demonstrate:

Fig. 1 shows a circuit of an ultrasonic transducer according to a first preferred embodiment;

Fig. 2 shows a circuit of an ultrasonic transducer according to a second preferred embodiment; and

... Figure 3 comparing a current measurement in a series circuit of the circuit of Figure 1 or Figure 2 and current in the series resonant circuit multiplied by the resistance value of a resistor R_S of the circuit;

FIG. 4 output signal of a control of the circuit from FIG. 1 or FIG. 2; and

Fig. 5, in a series circuit of the circuit of Fig. 1 or 2 stored energy in an active damping Fig. The method according to the invention.

In Fig. 1 shows a circuit of an ultrasonic transducer according to the invention. The ultrasonic transducer is used, for example, in parking systems for motor vehicles. The ultrasonic transducer comprises a membrane with a piezo element attached to it. An equivalent circuit diagram of the membrane is designated by reference number 1 . The equivalent circuit diagram comprises a series resonant circuit with an inductance L_S. a capacitance C_S and an ohmic resistor R_S and connected in parallel with a capacitance C0. In order to achieve a better temperature behavior due to the temperature response of the capacitance C0, a further capacitance C3 can be arranged in parallel to the series resonant circuit. When the piezo element is excited, the membrane is set in vibration and emits ultrasonic waves 2 . Ultrasound waves 3 reflected on an object set the membrane into vibrations, which is converted by the piezo element into a corresponding voltage or a corresponding current. The distance between the ultrasound transducer and thus the motor vehicle from the object can be determined from the transit time of the ultrasound waves ( 2 ) from transmission to reception of the reflected waves ( 3 ).

The circuit of the ultrasonic transducer according to the invention comprises a transformer with a primary coil L_1 and a secondary coil L_2 in order to supply a supply voltage U_V of z. B. to transform 12, 24 or 42 volts into an excitation voltage U_Err. The excitation voltage for an ultrasonic transducer for use in parking systems is approximately between 85 and 100 volts. The voltage generated in the circuit by the received ultrasound waves 3 is in the range of a few 100 microvolts. The received voltage is therefore orders of magnitude smaller than the excitation voltage.

Since the same membrane is used to transmit and receive ultrasonic waves, the converter is switched back and forth by a control device 4 between the transmission mode and the reception mode. In order to dampen the membrane vibrations after the emission of ultrasonic waves, active damping is provided. This means that after the transmission mode, the membrane vibrations are detected and the membrane is excited in phase (but with opposite amplitude) to the detected vibrations (ie countermeasures). This results in a particularly rapid decay of the vibrations and the membrane is ready to receive reflected ultrasound waves 3 after a short time.

In Fig. 5, the course of energy E contained in the series resonant circuit is shown. The stronger the vibrations of the membrane, the greater the energy E contained in the resonant circuit. To dampen the vibrations, the energy contained in the resonant circuit must be reduced as quickly as possible. In FIG. 5 it can clearly be seen that, due to the active damping, almost the entire energy E was withdrawn from the series resonant circuit after only about 1.3 milliseconds. The value of the energy E after 1.3 milliseconds corresponds approximately to the sensitivity limit E_limit of the circuit. It should be noted here that after approximately 0.9 milliseconds the active damping was ended by counter-control and the required residual damping takes place by a damping known per se from the prior art, which leads to an essentially linear decrease in the energy E. The high effectiveness of the active damping can be recognized from the steep drop in the course of the energy E within these 0.9 milliseconds. The time at which the active damping ends depends, inter alia, on the performance of the circuit used and on the maximum residual vibration of the ultrasound membrane to be achieved, which no longer disturbs the desired echo measurement of reflected ultrasound waves.

The active damping of the membrane vibrations is controlled by the control unit 4 . In the case of active damping, the membrane vibrations are detected and the countermeasures are carried out at different times from one another according to the invention. In FIG. 4, the course of a corresponding drive signal of the controller 4 U_B is shown for switching between engaging and countermeasures. The control signal U_B changes between LOW or 0 volts (no countermeasures or active detection of the membrane vibrations) and HIGH or approximately 550 millivolts (active countermeasures or no vibration detection). The value of 550 millivolts and / or the duty cycle can be tracked to the amplitude of the detected membrane vibration in order to adjust the strength of the countermeasures to the actual strength of the membrane vibrations still present.

In Fig. 3 is a comparison of the diaphragm 1 multiplies the measured current I_S the series resonant circuit voltage proportional U_A with the actual current flowing in the series resonant circuit current I_S illustrated with the resistance value of the resistor R_S the series resonant circuit. This multiplication is only necessary in order to be able to compare the same quantities - in this case, voltages. An overdrive of the output signal U_A of the current measuring circuit during countermeasures (signal from FIG. 4 to HIGH) can clearly be seen. During the detection of the membrane vibrations (no countermeasures, signal from FIG. 4 to LOW), the output signal U_A of the current measuring circuit largely corresponds to the current I_S or the voltage I_S.R_S at the resistor R_S. In this example, the amplitude of the current I_S through the series resonant circuit can thus be measured unaffected by the countermeasures in the negative half-wave.

The secondary coil L_2 of the transformer is by means of a antiparallel connected diode pairs D_1, D_2 of one Receiving circuit of the ultrasonic transducer decoupled. There Diodes have a reverse voltage of about 0.6 volts and that induced voltages from magnetic interference fields in the Usually less than 0.6 volts, the circuit is the Ultrasonic transducer by decoupling using the anti-parallel diode pairs D_1, D_2 particularly insensitive against magnetic interference fields. Higher voltages, e.g. the Excitation voltage U_Err, the diodes D_1, D_2 can easily happen.

A transformer is dispensed with in the circuit from FIG. 2. Instead, the excitation voltage U_Err is generated by an operational amplifier 5 from the supply voltage U_V. By completely dispensing with a transformer, the circuit becomes much more robust against magnetic interference fields.

Claims (10)

1. A method for operating an ultrasonic transducer for transmitting and receiving ultrasonic waves ( 2 ; 3 ) by means of a membrane, the membrane being excited for a predetermined period of time for transmitting ultrasonic waves ( 2 ), then the membrane vibrations are damped and for receiving ultrasonic waves ( 3 ) the membrane vibrations are detected, the membrane vibrations being detected as part of the damping and the membrane being excited in the opposite phase to the detected vibrations, characterized in that the detection of the membrane vibrations and the excitation of the membrane as part of the damping is carried out at different times , 2. The method according to claim 1, characterized in that to record the membrane vibrations within the scope of the Damping dependent on the membrane vibrations Current or voltage signal generated and in one Receiving circuit of the ultrasonic transducer is detected. 3. The method according to claim 2, characterized in that the membrane is operated in short-circuit mode and Detection of membrane vibrations as part of the damping a current signal is detected. 4. The method according to any one of claims 1 to 3, characterized in that a current or voltage signal (U_Err) for exciting the membrane with the help of an operational amplifier ( 5 ) is generated from a lower supply voltage (U_V). 5. The method according to any one of claims 1 to 3, characterized characterized that a current or voltage signal (U_Err) to excite the membrane using a Transformer from a lower supply voltage (U_V) is generated, with a secondary coil (L_2) of the Transformer from a receiving circuit of the Ultrasonic transducer is decoupled. 6. The method according to claim 5, characterized in that the secondary coil (L_2) of the transformer from the Receiving circuit of the ultrasonic transducer by a antiparallel diode pair (D_1, D_2) is decoupled. 7. Ultrasonic transducer for transmitting and receiving ultrasonic waves ( 2 ; 3 ) by means of a membrane, the ultrasonic transducer being the membrane, means for transmitting ultrasonic waves ( 2 ) by exciting the membrane for a predeterminable period of time, means for subsequently damping the membrane vibrations by detecting the Membrane vibrations and actuation of the membrane in the opposite phase to the detected vibrations and means for receiving ultrasonic waves ( 3 ) by detecting the membrane vibrations, characterized in that the detection of the membrane vibrations and the excitation of the membrane within the scope of the damping can be carried out at different times. 8. Ultrasonic transducer according to claim 7, characterized characterized in that the ultrasonic transducer means for Implementation of the method according to one of claims 2 to 6. 9. Use of an ultrasonic transducer according to claim 7 or 8 in a parking system for a motor vehicle. 10. Control device ( 4 ) for an ultrasound transducer for transmitting and receiving ultrasound waves ( 2 ; 3 ) by means of a membrane, the ultrasound transducer being the membrane, means for emitting ultrasound waves ( 2 ) by exciting the membrane for a predefinable period of time, means for the subsequent Damping the membrane vibrations by detecting the membrane vibrations and actuating the membrane in the opposite phase to the detected vibrations and means for receiving ultrasonic waves ( 3 ) by detecting the membrane vibrations, characterized in that the control device ( 4 ) has the means for detecting the membrane vibrations and the means actuated at different times to excite the membrane as part of the damping.