JPS623686A - Object detector - Google Patents

Abstract

PURPOSE:To reduce influences of temperature, humidity, or the like by substituting the variance of a stray capacity between a sensor consisting of an electrode member and an object to be detected with the variance of a frequency signal and detecting the frequency signal and viewing the fall state of a detected voltage signal to detect the approaching state of the object. CONSTITUTION:In an object detector, a differentiating circuit 9 which performs the differential processing of a detected voltage signal Vd' is provided in the preceding stage of a voltage variance detecting circuit 6. Time constants of delay elements Rd and Cd in the circuit 9 are set to large values to eliminate long-time variance components due to the change with time of temperature, humidity, or the like included in the detected voltage signal Vd'. The circuit 6 consists of a delay differential circuit 61 and a decision circuit 62 which decides whether the time width of an output signal Vo of the circuit 61 is longer than a preliminarily set value or not, and the circuit 62 judges the entrance of the object into a dangerous area to give an alarm command to a driver when the time width of the output signal is longer than the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an object detection device that detects the approach of an object such as an obstacle.

BACKGROUND ART Recently, as an object detection device used for detecting obstacles when a car is running, for example, as shown in FIG. A device has been developed in which the sensor is mounted in a line along the inside of a bumper 11, such as a manufactured vehicle, and detects the approaching state of an object based on the change in stray capacitance between the sensor 1 and the obstacle. (See Japanese Patent Application No. 58-220412).

FIG. 5 is a circuit diagram showing the basic principle of object detection. When an AC signal is applied to a series circuit of electrode member 1 and resistor R, the stray capacitance C between sensor 1 and object 0 varies depending on the distance between them. Focusing on the change in AC output voltage at which voltage dividing point of sensor 1 and resistor R changes, sensor 1 detects the falling state of the output voltage when object ○ approaches it, and determines the approaching state of object ○. We are trying to detect this.

Figure 6 shows an object detection device constructed based on this basic principle, which consists of an oscillator 2 that generates an alternating current signal of a constant frequency, and a resistor divider installed in parallel on the output side of the oscillator 2. A network 3 consisting of a circuit, a sensor l connected to a dividing point of the network 3, a band filtering amplifier 4 that performs noise removal and amplification of the AC output voltage from the network 3, and a band reduction amplifier 4 that removes noise from the AC output voltage from the network 3 and amplifies the amplified output signal. a detection circuit 5 that performs wave detection; a voltage fluctuation detection circuit 6 that detects the approaching state of object ○ from the falling state of the detected voltage signal and detects if there is a voltage drop that exceeds a preset condition; A driver 7 controls the operation of the alarm device 8 according to the detection signal.

With this configuration, when an AC signal with a constant frequency FO is applied from the oscillator 2 to the network 3, the AC signal is appropriately attenuated in proportion to the proximity of the object ○ facing the sensor 1. The signal is sent to a bandpass filtering amplifier 4, where noise induced in the sensor 1 etc. is removed and only the alternating current component of the frequency FO is amplified. Then, the predetermined amplified AC signal is detected by a detection circuit 5, and a DC voltage signal corresponding to the amplitude of the AC signal is sent to a voltage fluctuation detection circuit 6. The voltage fluctuation detection circuit 6 detects a falling state of the applied DC voltage signal, and
When the degree of voltage drop falls below a preset reference value, the driver 7 determines that object ○ has entered the dangerous area.
give an alarm command. Thereby, the alarm device 8 is configured to issue an alarm to that effect, such as by sounding or being driven to turn on.

In an object detection device that detects an object based on changes in stray capacitance as described above, it is undeniable that the detected voltage fluctuates over a long period of time due to temporal changes in temperature or humidity. Therefore, it has a negative effect on object detection.

1. The present invention has been made in consideration of the above points, and its first purpose is to remove long-term fluctuation components contained in the detected voltage and to detect objects without being affected by temperature or humidity. The object of the present invention is to provide an object detection device that can perform the following operations.

A second object of the present invention is to provide an object detection device capable of eliminating a decrease in object detection sensitivity that is caused by removing long-term fluctuation components contained in the detected voltage. It is.

In order to achieve the first objective, the present invention replaces a change in stray capacitance between a sensor made of an electrode member and an object to be detected with a change in a frequency signal, and detects the frequency signal. , which detects the approaching state of an object by looking at the falling state of the detected voltage signal, and in particular performs differential processing on the detected voltage signal to remove long-term fluctuation components contained in the voltage signal. I am trying to take measures to prevent this.

Further, in order to achieve the second object, the present invention short-circuits the differential element in the differential processing means for a certain period of time at the initial stage of power-on, thereby reducing object detection sensitivity until the differential capacitor is fully charged at power-on. We are taking measures to prevent this.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In the object detection device according to the present invention having the configuration shown in FIG. 6, as shown in FIG.
The present invention is characterized in that it is provided with a differentiation circuit 9 that performs differentiation processing.

Here, the time constants of the delay elements Rc[, Cd in the differentiating circuit 9 are set large to remove long-term fluctuation components caused by temporal changes in temperature or humidity contained in the detected voltage signal Vd'. I'm trying to do that.

In addition, in the configuration shown in FIG. 1, the voltage fluctuation detection circuit 6 includes a delay differential circuit 61 and determines whether or not the time width of its output signal vO is the same as a preset time width. A determination circuit 62 is used. Note that the comparator CMP in the delay differential circuit 61
When the input voltage on the negative polarity side is V + - and the input voltage on the ten polarity side is v2, a low level output is produced when v1≧v2.

The offset voltage is adjusted to produce a high level output when Vl<V2.

In such a voltage fluctuation detection circuit 6, as shown in FIG. 2, when the differentiated voltage signal Vd' falls in a period T, one input voltage v1 in the comparator CMP decreases in the same period. However, the other input voltage v2 falls with a certain delay Td, and as a result, Vl<V2 for a period of T0Td, and the output V
o becomes high level. Therefore, the voltage signal V d'
Since the falling period T changes depending on the degree of approach of the object to the sensor 1, when the time width of the delay differential circuit 61 exceeds a predetermined value, the determination circuit 62 determines that the object has entered the dangerous area. so that an alarm command is given to the driver 7. Note that when the position of the object relative to the sensor 1 does not change and the voltage signal Vd' becomes constant, V1=V2, and when the object moves away from the sensor 1, Vl>■2, and the comparator C
The output of the MP becomes low level, and no alarm command is issued at that time.

Further, in the case of adopting the configuration shown in FIG. 1, when the power of the object detection device is turned on, a bias voltage Vcc is applied to the differentiating circuit 9, thereby supplying a charging current to the capacitor Cd through the resistor Rd. . In that case, delay element C
Since the time constants of d and Rd are set to large values (on the order of several seconds) as described above, it takes quite a long time until the capacitor Cd is fully charged. Therefore, the object detection sensitivity becomes low during the charging period of the capacitor Cd, and as a result, the object detection device remains in a low sensitivity state for a considerable period of time after being powered on.

Therefore, the present invention takes measures to significantly shorten the period during which the object detection device is in a state of decreased sensitivity when the power is turned on.

FIG. 3 shows an embodiment in such a case, in which an analog switch SW is provided in parallel with the resistor Rd in the differentiating circuit 9, and a timer circuit 12 controls the ON time of the analog switch SW when the power is turned on. I have to.

That is, when the tWX of the object detection device is turned on, the bias voltage Vcc is applied to the differentiating circuit 9, and the bias voltage V'cc is also applied to the timer circuit 12.

At the initial stage when the bias voltage Vcc is applied to the timer circuit 12, the capacitor Ct is not yet in a charged state, so the output of the inverter INV becomes a high level LrH17, which turns on the analog switch SW and activates the differential circuit. Short-circuit the resistor Rd at 9. Therefore, while the analog switch SW is on, the capacitor Cd in the differentiating circuit 9 is charged through the analog switch SW, and is quickly fully charged to compensate for the decrease in object detection sensitivity during this period.

Thereafter, the capacitor Ct in the timer circuit 12 is fully charged, and the output of the inverter INV at that time becomes a low level #L Hp, which turns off the analog switch SW and restores the short-circuited state of the resistor Rd in the differentiating circuit 9. is released, and thereafter the differentiating circuit 9 begins to perform normal differentiating processing on the voltage signal (d) sent to it.

As described above, the object detection device according to the present invention includes a means for replacing a change in stray capacitance between a sensor made of an electrode member and an object to be detected with a change in a frequency signal, and a means for detecting the frequency signal. means for differentially processing the detected voltage signal, and means for detecting the approaching state of an object by looking at the falling state of the differentially processed voltage signal. It has the excellent advantage of being able to remove long-term fluctuation components and detecting objects without being affected by temperature, humidity, or the like.

Further, in the present invention, in particular, means is provided for short-circuiting the differential element in the differential processing means for a certain period of time at the initial stage of power-on.

This has the excellent advantage of eliminating a drop in object detection sensitivity when the power is turned on, which is caused by removing long-term fluctuation components contained in the detected voltage.

[Brief explanation of drawings]

FIG. 1 is an electrical wiring diagram showing the configuration of the differential circuit and voltage fluctuation detection circuit portion in one embodiment of the object detection device according to the present invention, and FIG. 2 is a time chart of signals of each part of the voltage fluctuation detection circuit in the same embodiment. , FIG. 3 is an electrical wiring diagram showing the configuration of the differential circuit and voltage fluctuation detection circuit portion in another embodiment of the present invention, FIG. 4 is a diagram showing an example of the installation state of the sensor in the object detection device, and FIG. The figure is a circuit diagram showing the basic principle of object detection, and FIG. 6 is a block diagram showing an example of the configuration of a conventional object detection device. 1... Sensor 2... Oscillator 3... Network 4... Bandwidth filter amplifier 5... Detection circuit 6...
・Voltage fluctuation detection circuit 7... Driver 8... Alarm device 9... Differential circuit 12... Timer circuit

Claims (1)

[Claims] 1. means for replacing a change in stray capacitance between a sensor made of an electrode member and an object to be detected with a change in a frequency signal, a means for detecting the frequency signal, and a means for detecting the frequency signal; An object detection device comprising means for differentially processing a voltage signal obtained by differential processing, and means for detecting an approaching state of an object by observing a falling state of the differentially processed voltage signal. 2. Means for replacing a change in stray capacitance between a sensor made of an electrode member and an object to be detected with a change in a frequency signal, a means for detecting the frequency signal, and a differential process for the detected voltage signal. means for detecting the approaching state of an object by looking at the falling state of the differentiated voltage signal, and means for short-circuiting the differential element in the differential processing means for a certain period of time at the initial stage of power-on. Detection device.