JP4752846B2 - Obstacle detection device - Google Patents

Description

  The present invention relates to an obstacle detection apparatus.

  Conventionally, there has been provided an obstacle detection device that detects the presence of an obstacle by transmitting an ultrasonic wave to a detection range and receiving a reflected wave reflected by the obstacle.

  As an obstacle detection device of this type, an ultrasonic transducer including a plurality of receiving piezoelectric elements for receiving reflected waves is used, and the output of each receiving piezoelectric element is compared by comparing the output of each receiving piezoelectric element. Some can detect direction as well. For example, in the case of an obstacle detection device using two piezoelectric elements 1 as shown in FIG. 3, one piezoelectric element 1 intermittently sends ultrasonic pulses toward the detection range as a piezoelectric element for transmission. The two piezoelectric elements 1 receive the reflected waves reflected by the obstacle T existing in the detection range as the receiving piezoelectric elements.

  The operation of this obstacle detection apparatus will be described in detail with reference to FIG. 4A shows the waveform of the input signal to the transmitting piezoelectric element, FIG. 4B shows the waveform of the received signal by the output of one piezoelectric element 1, and FIG. The waveform of the received signal by the output of the other piezoelectric element 1 is shown. 4B and 4C, L1 and L2 are reverberation components, and E1 and E2 are components of reflected waves reflected by the obstacle T. The distance L to the obstacle T can be detected by the time t1 from when the ultrasonic wave is transmitted until the reflected wave is received, and the time until one piezoelectric element 1 receives the ultrasonic wave and the other The obstacle detection device and the obstacle T are connected to a plane whose normal is a straight line along the direction in which the piezoelectric elements 1 are arranged, from the difference t2 from the time until the piezoelectric element 1 receives the ultrasonic wave. The angle θ formed by the straight line can be detected. For example, as shown in FIG. 5, a plurality (two in the figure) of such obstacle detection devices are attached to the front portion of the vehicle C, and detect the obstacle T in the detection range Z in front of the vehicle C. Used for. Since the direction of the obstacle T can be detected, it is more accurately detected whether the obstacle T exists on the course of the own vehicle, compared to an obstacle detection device that simply detects the distance to the obstacle T. be able to.

  As an obstacle detection apparatus provided with two piezoelectric elements 1 as described above, for example, there is one shown in FIG. 6 (see, for example, Patent Document 1). The obstacle detection device includes a vibration case 2 as a vibrating body made of a conductive material and provided with two storage recesses 21 arranged side by side, and a piezoelectric element 1 stored in each storage recess 21.

  More specifically, the vibration case 2 is made of, for example, a metal such as aluminum, and has an oval flat plate portion 26 and two pieces that are arranged in the longitudinal direction on the back surface of the flat plate portion 26 with a gap between them. And a cylindrical portion 24. The piezoelectric element 1 is bonded (fixed) to the portion surrounded by the cylindrical portion 24 on the back surface (the lower surface in FIG. 6) of the flat plate portion 26 with an adhesive B (see FIG. 7). A storage recess 21 is formed in a portion surrounded by the cylindrical portion 24, and a partition recess 23 is formed between the two cylindrical portions 24. Further, the surface of the flat plate portion 26 (upper surface in FIG. 6) is an exit / incident surface 22 through which ultrasonic waves are emitted and incident.

  The piezoelectric element 1 is formed in a disk shape, and has electrodes 11 and 12 made of a conductive material such as metal, respectively, on both surfaces of a body portion 10 made of piezoelectric ceramic as shown in FIG. One electrode 11 of the piezoelectric element 1 is brought into contact with the bottom surface of the housing recess 21 of the vibration case 2 and drawn out through the vibration case 2 and the lead wire 6, and the other electrode 12 is drawn out through the lead wire 6. These are respectively connected to external circuits for analyzing the output of the piezoelectric element 1 and used for receiving ultrasonic waves. That is, in the vibration case 2, the bottom of each storage recess 21 is a diaphragm in the claims. An adhesive B having no electrical conductivity is interposed between the vibration case 2 and the piezoelectric element 1. However, since the vibration case 2 has fine irregularities, the electrode 11 of the piezoelectric element 1 vibrates. Contact conduction is made to the convex and concave portions of the case 2. Here, one piezoelectric element 1 is also connected to a drive circuit for generating ultrasonic waves, and is used for transmitting ultrasonic waves. That is, each piezoelectric element 1 is a receiving piezoelectric element, and the piezoelectric element 1 connected to the drive circuit also serves as a transmitting piezoelectric element. That is, one piezoelectric element 1 connected to the drive circuit and driven when an obstacle is detected is the first piezoelectric element in the claims, and the other piezoelectric element 1 is the second piezoelectric element in the claims. Further, the partition recess 23 is provided between the storage recess 21 in which the transmitting piezoelectric element is stored and the storage recess 21 in which the receiving piezoelectric element is stored, on the opposite surface of the exit / incident surface 22. become. Further, each storage recess 21 is filled with a buffer filler 3 for suppressing reverberation.

  Further, the housing 4 is formed in a bottomed cylindrical shape having an oval cross section, and the vibration case 2 is accommodated in the housing 4 so that the exit / incident surface 22 is exposed from the opening of the housing 4.

In addition, between the housing 4 and the vibration case 2, there is a holding body 5 made of an elastic material such as synthetic rubber, which has a higher sound absorption coefficient for the ultrasonic waves generated by the transmitting piezoelectric element than the material of the vibration case 2. Is provided. The holding body 5 is provided with two holding recesses 51 arranged side by side. The outer circumference of the holding body 5 is formed to be the same as the inner circumference of the housing 4, and the inner circumference of the holding recess 51 is formed to be the same as the outer circumference of the cylindrical portion 24 of the vibration case 2. Each cylindrical portion 24 of the vibration case 2 is press-fitted into the holding recess 51, and the holding body 5 is press-fitted into the housing 4, whereby the vibration case 2 is held in the housing 4. In addition, a sound absorbing portion 52 that is housed in the partition recess 23 and absorbs reverberation between the piezoelectric elements 1 is provided at a portion that partitions the two holding recesses 51 in the holder 5.
JP 2004-253911 A

  In the obstacle detection apparatus as described above, when the period in which the piezoelectric element 1 is not driven is a long period of time, for example, several years, the duration of reverberation components indicated by L1 and L2 in FIGS. , Referred to as “reverberation time”) may be longer than during manufacture. When the reverberation time is thus extended, the reflected wave components indicated by E1 and E2 in FIGS. 4B and 4C are buried in the reverberant component, so that the reflected wave component and the reverberant component are distinguished. There is a high possibility of false detection and detection omission due to the loss of

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide an obstacle detection apparatus capable of eliminating the extension of the reverberation time.

The invention according to claim 1 is an obstacle detection device that detects an obstacle within a predetermined detection range by transmitting and receiving ultrasonic waves, and is made of a conductive material, and ultrasonic waves are emitted and incident toward the detection range. Two diaphragms having exit / incident surfaces, and one diaphragm for each diaphragm so that electrodes are provided on both sides in the thickness direction and one electrode is in contact with the opposite side of the exit / incident surface of the diaphragm The first and second piezoelectric elements that are fixed together and the first piezoelectric element are driven to generate ultrasonic waves, and each diaphragm receives a reflected wave that is reflected in the detection range. And a control unit that performs a detection operation for detecting an obstacle based on an electric signal generated in each piezoelectric element, and the second piezoelectric element is a receiving piezoelectric element for receiving a reflected wave. , the control unit, before performing the detection operation, less the And performing a preliminary operation of driving the second piezoelectric element.

  According to the present invention, the extension of the reverberation time due to long-term nonuse is eliminated to some extent by the preliminary operation.

  The invention of claim 2 comprises, in the invention of claim 1, an input / output unit that constitutes a transmission / reception block together with the piezoelectric element by amplifying an electrical signal between each piezoelectric element and the control unit, The control unit is characterized by detecting an abnormality of each transmission / reception block based on the output of each piezoelectric element input via the input / output unit during the preliminary operation.

  According to the present invention, the preliminary operation can be effectively used for detecting an abnormality.

  According to the invention of claim 1, since the control unit performs a preliminary operation for driving at least the second piezoelectric element before performing the detection operation, the reverberation time extension due to long-term non-use is caused by the preliminary operation. It is solved to some extent.

  According to the invention of claim 2, since the control unit detects an abnormality of each transmission / reception block based on the output of each piezoelectric element input via the input / output unit during the preliminary operation, the preliminary operation is performed. It can be effectively used for detecting anomalies.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  Since the basic configuration of this embodiment is the same as that of the conventional example, common portions are denoted by the same reference numerals, description thereof is omitted, and only different portions are described.

  The present embodiment is an obstacle detection device mounted on a vehicle. As shown in FIG. 1, each of the embodiments has a piezoelectric element 1, and an ultrasonic wave for a predetermined detection range Z (see FIG. 5) is detected by the piezoelectric element 1. Two transmission / reception blocks 7 capable of transmitting and receiving waves and a control unit 8 for controlling each transmission / reception block 7 are provided. The power of each part is supplied from a battery (not shown) mounted on the vehicle.

  Each transmission / reception block 7 amplifies a piezoelectric element 1 and a transmission side amplification that amplifies a transmission signal that is an electric signal output from the control unit 8 to drive the piezoelectric element 1 to transmit ultrasonic waves. A circuit 71, a reception side amplification circuit 72 that amplifies a reception signal that is an electric signal generated in the piezoelectric element 1 due to reverberation or a vibration due to a reflected wave, and a reception signal amplified by the reception side amplification circuit 72 And a detection circuit 73 for generating a signal to be input to the control unit 8. That is, each piezoelectric element 1 shown in FIG. 6 is included in a different transmission / reception block 7. In each transmission / reception block 7, the transmission side amplification circuit 71 and the reception side amplification circuit 72 are respectively shown in FIG. 6. It is electrically connected to both electrodes of the piezoelectric element 1 via the pair of lead wires 6 shown. As shown in FIG. 2, the detection circuit 73 compares the amplitude of the reception signal input from the reception side amplification circuit 72 with a predetermined discrimination threshold, and during a period in which the amplitude of the reception signal is equal to or greater than the discrimination threshold. The output is set to H level, and the output is set to L level during the period when the amplitude of the received signal is less than the discrimination threshold. In FIG. 2, the reverberation component L1 in one transmission / reception wave block 7 is taken as an example, but the operation for the reflected wave components E1 and E2 and the operation in the other transmission / reception block 7 are the same. The control unit 8 determines the times t1 and t2 used in the operation described with reference to FIG. 4 with the rising timing that can be determined to correspond to the reflected wave among the rising edges of the output of the detection circuit 73 as the timing at which the reflected wave is received. . That is, the transmission side amplification circuit 71, the reception side amplification circuit 72, and the detection circuit 73 constitute an input / output unit in the claims. The transmission side amplification circuit 71 and the reception side amplification circuit 72 may include a filter circuit for removing noise. Further, when the piezoelectric element 1 and the control unit 8 are disposed at positions separated from each other, a plurality of stages of the transmission side amplification circuit 71 and the reception side amplification circuit 72 may be provided.

  The control unit 8 performs obstacle detection (detection operation) by each of the transmission / reception blocks 7 in accordance with a control signal input from the outside. The contents of the detection operation are as described with reference to FIGS. 3 and 4. One of the appropriate piezoelectric elements 1 in the transmission / reception block 7 is a transmission piezoelectric element, and the control unit 8 is used for transmission. The piezoelectric element 1 is driven by a separate excitation method by inputting, for example, a 72 kHz rectangular wave as a transmission signal to the piezoelectric element 1 as a piezoelectric element via the transmission side amplification circuit 71. The control signal indicates, for example, the operating state of the engine, the state of a detection switch that is turned on and off by manual operation to instruct on / off of the detection operation, the traveling direction and speed of the vehicle, and the power supply voltage. The control unit 8 is such that the engine is operating, the detection switch is turned on, the traveling direction of the vehicle is the direction of the detection range Z, and the vehicle speed is equal to or less than a predetermined operation speed (for example, 10 km / hour). In addition, the power supply voltage of the battery is periodically detected only during a period higher than a predetermined operation voltage required for the detection operation (for example, 7 V when the rated voltage of the obstacle detection device is 9 to 15 V). Perform the action. When an obstacle is detected as a result of the detection operation, a notification signal indicating the direction of the detected obstacle and the distance to the obstacle is output. The notification signal is used for controlling a load (not shown) for notification to the user, such as a liquid crystal display or an alarm buzzer.

  In addition, the present embodiment is characterized in that the control unit 8 performs a preliminary operation for driving the piezoelectric elements 1 of the respective transmission / reception blocks 7 after the start (power-on) and before the detection operation. Specifically, the control unit 8 performs a preliminary operation when at least one piece of information indicated in the control signal changes from a state where the detection operation should not be performed to a state where the detection operation should be performed. . That is, the timing at which the controller 8 performs the preliminary operation includes the timing at which the engine is started, the timing at which the detection switch is turned on, the timing at which the vehicle starts moving in the direction of the detection range Z, The timing when the moving speed of the vehicle in the direction has changed from a higher state to a lower state than a predetermined preliminary speed (for example, 25 km / h when the operating speed is 10 km / h as described above) set slightly higher than the operating speed. Or the timing when the power supply voltage changes from a lower state to a higher state than the operating voltage can be considered. The detection operation is performed when all of the above conditions such as the engine operation, the detection switch, the moving direction and moving speed of the vehicle, and the power supply voltage are satisfied, and other conditions are satisfied after the engine is started. By the time, it is almost impossible that the reverberation time will be extended (that is, for many years), so the controller 8 may perform the preliminary operation only when the engine is started. The frequency of the rectangular wave output from the control unit 8 to drive the piezoelectric element 1 during the preliminary operation is 72 kHz, for example, as in the detection operation. The driving of the piezoelectric element 1 in the preliminary operation is performed for each wave transmitting / receiving block 7, for example. Each is performed 5 times every 5 ms by 250 μs.

  According to the inventor's experiment, the preparatory operation as described above shortens the reverberation time that has become longer due to long-term non-use as described in the section of the problem (that is, the reverberation time extension is solved to some extent). Has been confirmed). The inventor reduces the reverberation time as described above by changing the state of the contact surface between the electrode 11 of the piezoelectric element 1 and the vibration case 2 in accordance with the vibration caused by the driving of the piezoelectric element 1. This is considered to be due to the change in the electrical connection state between 11 and the vibration case 2.

  Here, in the preliminary operation, it is not always necessary to drive both piezoelectric elements 1, but when one piezoelectric element 1 (the first piezoelectric element in the claims) is always a piezoelectric element for wave transmission, the other piezoelectric element 1 is used. Since the reverberation time tends to be long in the element 1 (second piezoelectric element in the claims), it is necessary to drive at least the other piezoelectric element 1 in the preliminary operation.

  Further, in the present embodiment, the abnormality of each transmission / reception block 7 is also detected in the preliminary operation. Specifically, the control unit 8 detects the output due to reverberation accompanying the driving of the piezoelectric element 1 in the preliminary operation from each of the transmission / reception blocks 7, and drives the piezoelectric element 1 for all the five times of driving in the preliminary operation. If the output of the detection circuit 73 is L level during the period of 600 μs to 800 μs after the start of the reception, the reception portion of the transmission / reception block 7 including the detection circuit 73 (that is, the piezoelectric element 1 or the reception side amplification circuit 72 or It is determined that there is an abnormality in the detection circuit 73 or the electrical connection between them. However, when it is determined that there is an abnormality in the receiving portions of all the transmitting / receiving blocks 7 with respect to the driving of the piezoelectric element 1 of one transmitting / receiving block 7, the control unit 8 receives the receiving signals of each transmitting / receiving block 7. It is determined that there is an abnormality in the transmission part of the transmission / reception block 7 including the driven piezoelectric element 1 (that is, the piezoelectric element 1 or the transmission side amplification circuit 71 or the electrical connection between them) instead of the wave part. When it is determined that there is some abnormality, the control unit 8 outputs a notification signal indicating information on a portion determined to have an abnormality to the outside. In addition, when a preliminary operation is performed, for example, when the engine is started or when the detection switch is turned on in a state where it is determined that there is an abnormality, the driving of the piezoelectric element 1 is started for all five driving operations in the preliminary operation. After that, if the output of the detection circuit 73 is at the H level during the period of 600 μs to 800 μs, the control unit 8 determines that the abnormality has been recovered and outputs a notification signal indicating the recovery from the abnormality. The notification signal output during the preliminary operation as described above is used for controlling a notification load (not shown) such as a liquid crystal display, similarly to the notification signal output when an obstacle is detected.

  Further, in a system using a plurality of obstacle detection devices, the above-described notification signal indicating an abnormality is used as a control signal in another obstacle detection device, and an abnormality is detected in any obstacle detection device constituting the system. The detection operation may be performed only when it is not. In this case, when a control signal (notification signal) indicating a return is input from an obstacle detection device in which an abnormality is detected only in the system (that is, the obstacle detection device in which an abnormality is detected is in the system). The control unit 8 may perform a preliminary operation when the state is changed from the state existing in (1) to the state not existing.

  As shown in FIG. 6, instead of fixing the piezoelectric elements 1 of the transmission / reception blocks 7 to the common vibration case 2 (that is, each vibration plate in the claims is composed of one vibration case 2) You may fix to the vibration case 2 (that is, each diaphragm in a claim is comprised in the separate vibration case 2). Even in this case, for example, each resonating case 2 may be held by a common holding body 5 so that reverberation due to vibration of one piezoelectric element 1 can be detected by other piezoelectric elements 1. For example, it is possible to determine abnormality by the preliminary operation.

It is a block diagram which shows embodiment of this invention. It is explanatory drawing which shows operation | movement of a detection circuit same as the above. It is explanatory drawing which shows an example of operation | movement of an obstruction detection apparatus. It is explanatory drawing which shows an example of operation | movement of an obstruction detection apparatus, (a) is the input signal waveform to the piezoelectric element for transmission, (b) is the output signal waveform of one piezoelectric element, (c) is the other piezoelectric element. The output signal waveform of an element is shown. It is explanatory drawing which shows an example of the usage method of an obstruction detection apparatus. It is sectional drawing which shows the principal part of an example of an obstruction detection apparatus. It is explanatory drawing which shows the connection state of a piezoelectric element and a vibration case.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2 Vibration case 7 Transmission / reception block 8 Control part 11,12 Electrode 22 Outgoing / incident surface 71 Transmission side amplification circuit 72 Reception side amplification circuit 73 Detection circuit

Claims (2)

An obstacle detection device that detects an obstacle within a predetermined detection range by transmitting and receiving ultrasonic waves,
Two diaphragms made of a conductive material and having an exit / incident surface that emits and enters an ultrasonic wave directed toward the detection range;
First and second piezoelectric elements fixed to each diaphragm so that electrodes are provided on both surfaces in the thickness direction and one electrode is in contact with and conductive to the opposite surface of the diaphragm. When,
The first piezoelectric element is driven to generate an ultrasonic wave, and each diaphragm receives a reflected wave reflected by the ultrasonic wave in the detection range, thereby causing an obstacle based on an electric signal generated in each piezoelectric element. A control unit that performs a detection operation for detecting an object,
The second piezoelectric element is a receiving piezoelectric element for receiving the reflected wave,
The obstacle detection apparatus, wherein the control unit performs a preliminary operation of driving at least the second piezoelectric element before performing the detection operation. For each piezoelectric element, it comprises an input / output unit interposing between each control unit and amplifying an electrical signal to constitute a transmission / reception block together with the piezoelectric element,
2. The obstacle detection device according to claim 1, wherein the control unit detects an abnormality of each transmission / reception block based on an output of each piezoelectric element input via the input / output unit during preliminary operation. .

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