JPH0821723B2 - Capacitive array type ultrasonic proximity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is installed in a robot or various industrial equipment to measure a distance to a target object at a relatively short distance, or to measure the size of the target object. The present invention relates to a capacitive array type ultrasonic proximity sensor used when recognizing a sheath shape.

[Conventional technology]

In recent years, inexpensive and high-performance microcomputers have spread, and automation or robotization is being promoted in various industrial fields by using them. However, robots or automatic devices currently in practical use can only carry out work such as lifting or carrying a certain fixed shape, fixed size, or fixed weight, or processing, assembling, etc. by a certain program. The current situation is that it cannot be done. On the other hand, due to the diversification of consumers, the trend of high-mix low-volume production has become stronger, and FMS (Flexible Manufacturing System: Flexible Manufacturin
g System) is called for the development of automation technology. In such a flow of automation, it is necessary to equip a robot or an automatic machine with various sensors in place of human sensory organs and perform accurate control based on the information from them. Assuming that the robot picks up an object, first the object is found by the visual sensor, then the object is approached with the help of the proximity sensor, and finally the hardness of the object, the object by the tactile sensor. It measures the repulsive force when grasping an object and controls the grasping force while lifting the object. Among the sensors that assist these operations, the proximity sensor is considered to play a role in measuring distance information, which is difficult with a visual sensor, and high-speed object supplementation. Various types of proximity sensors have been proposed so far, but ultrasonic sensors are generally considered to be superior.

[Problems to be solved by the invention]

As an example of the ultrasonic sensor, there is a capacitive array ultrasonic sensor described in Japanese Patent Application No. 60-289290 as shown in FIG. 4 (a) is a plan view of the capacitive array type ultrasonic sensor, and FIG. 4 (b) is a sectional view taken along line AB. The structure of the sensor part of this array type ultrasonic sensor is simple, and an organic film such as a polyester film in which a metal 405 is vapor-deposited on one surface on an electrode 403 arranged in an array on the silicon substrate 401 via a silicon oxide film 402. It is a simple structure with 404 attached. In such an array type ultrasonic sensor in which a plurality of ultrasonic elements are arranged in an array,
An air layer trapped between the array of electrodes 403 and the organic film 404 can be vibrated by electrostatic force to generate ultrasonic waves in the air. Further, the ultrasonic waves propagating in the air can be detected by vibrating the organic film 404 and detecting a capacitance change between the organic film 404 and the arrayed electrodes 403. Driving this kind of ultrasonic sensor requires an AC signal with a large voltage during ultrasonic wave transmission, while capturing very small membrane vibrations during ultrasonic wave reception and amplifying to the level required for signal processing. Therefore, a high-sensitivity amplifier with less noise is required.

Conventionally, in order to perform such an operation with one capacitive array type ultrasonic sensor, as shown in FIG. 5, a transmitting side signal processing circuit 501 and a receiving side signal are provided for each ultrasonic element 504. A processing circuit 502 is provided, and these signal processing circuits are switched by a switch 503.
To the ultrasonic element 504 via switchable connection, each transmission side signal processing circuit 501 is connected to the signal source 505, each reception side signal processing circuit 502 is connected to the adder 506, the transmission side signal Processing circuit
The 501 and the receiving side signal processing circuit 502 are used by switching between transmitting and receiving.

In this type of capacitive array ultrasonic sensor, a large-amplitude AC signal during ultrasonic wave transmission leaks into the receiving circuit, and in order to avoid it, it is sufficient to switch between transmitting and receiving waves. It is necessary to have a time margin and there is a time delay for switching the switch, which has hindered the improvement of the short-distance measurement performance of the capacitive array type ultrasonic sensor. For example, frequency
When a distance measurement experiment was conducted by emitting 5 sine waves of 100 kHz (wavelength 3.4 mm), the distance to the object could be measured only up to about 100 mm.

An object of the present invention is to provide a capacitive array type ultrasonic wave proximity sensor capable of eliminating the above-mentioned conventional drawbacks and improving the short distance measurement performance.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a capacitive array type ultrasonic proximity sensor capable of transmitting and receiving ultrasonic waves, wherein some ultrasonic waves of the capacitive ultrasonic elements forming the array are used. The element is an ultrasonic element exclusively used for receiving waves, in which a source follower circuit is built in the output section, and the remaining ultrasonic elements are exclusively used for transmitting waves.

[Action]

According to the principle of the present invention, a large number of ultrasonic elements forming an electrostatic capacitance array type ultrasonic proximity sensor share the roles of an ultrasonic wave transmitting element and an ultrasonic wave receiving element, Has a built-in source follower circuit at its output. As a result, a drive circuit that generates a large-amplitude AC signal is connected to the transmitting element without interference between the elements,
A high-sensitivity amplifier with low noise can be connected to the wave receiving element. That is, since the circuits of the transmitting and receiving parts of the ultrasonic wave are completely separated, the possibility of interference due to the transmitting ultrasonic wave directly entering the adjacent wave receiving element depends on the wavelength used and the adjacent transmitting and receiving wave. It can be reduced by appropriately selecting design parameters such as the distance between elements. Therefore, the signal for driving does not leak into the signal amplifier circuit, both circuits can be driven at the same time, and it becomes possible to measure a short distance in a short time until the reflected wave from the object is received. Further, the wave receiving element has a built-in source follower circuit at its output. The source follower circuit is used as an impedance converter having high input impedance and low output impedance. By using this as the receiver of the capacitive ultrasonic element of the present invention, it becomes possible to capture the electric signal output from the high impedance sensor with a good S / N ratio and input it to the amplifier circuit. In addition, it becomes possible to connect the impedance converter to the ultrasonic element on-chip.

〔Example〕

 The present invention will be described below based on examples.

FIG. 1 is a schematic configuration diagram of a capacitive array type ultrasonic proximity sensor for explaining an embodiment of the present invention. p
A total of 32 elements, 16 in number each of receiving-side ultrasonic elements 102 and transmitting-side ultrasonic elements 103, are arranged on a silicon substrate 101 of the mold.

An impedance conversion circuit composed of a MOS type FET shown in FIGS. 2A and 2B is formed near the electrode output pad of the receiving side ultrasonic element 102. Incidentally, FIG. 2 (a)
Shows the configuration of the impedance conversion circuit section, and FIG. 2 (b) shows its equivalent circuit.

In FIG. 2, the first transistor 201 is a depletion type MOSFET that receives an ultrasonic wave reception signal with high impedance. On the other hand, the second transistor 202 functions as a load resistance. These transistors were first formed on a silicon substrate by a standard manufacturing process, and then an ultrasonic sensor as shown in FIG. 4 was formed. However, the gate of the first transistor 201 was formed at the same time after the electrode of the receiving-side ultrasonic element was formed. In FIG. 2A, 203 is an ultrasonic wave receiving element electrode, and 204 is an output pad of the receiving side ultrasonic element. In FIG. 2B, 205 is an output unit and 206 is a receiving-side ultrasonic element.

FIG. 3 is a final block diagram of the capacitive array type ultrasonic proximity sensor obtained in this manner. In the figure, reference numeral 301 denotes a transmitting-side ultrasonic element, a transmitting-side signal processing circuit 302 is connected to each transmitting-side ultrasonic element, and these signal processing circuits are connected to a signal source 303. Since the capacitive array type ultrasonic proximity sensor of the present embodiment is operated for the purpose of electronically scanning the ultrasonic beam in a fan shape, the transmitting side signal processing circuit 302 is provided with a programmable delay circuit. ing.

On the other hand, in the figure, 304 is a receiving-side ultrasonic element, and each receiving-side ultrasonic element is connected to the impedance conversion circuit 305 composed of the MOSFET described in FIG. The receiving side signal processing circuit 306 is connected, and these signal processing circuits are connected to the adder 307. The receiving side signal processing circuit 306 is composed of a low noise amplifier, a delay circuit and the like. This delay circuit receives the signal returned by the ultrasonic wave transmission beam by electronic scanning reflected by the target object and performs delay processing opposite to that at the time of wave transmission to synthesize the signal from each ultrasonic element. is necessary. The battery symbol in FIG. 3 indicates a DC bias power source necessary for extracting a signal from the electrostatic electroacoustic transducer. Generally, when a voltage is applied between the diaphragm and the fixed electrode, the electrostatic converter vibrates the air by the electrostatic force that acts between the electrodes (in the case of an electrostatic speaker), or conversely, a force is applied between the electrodes. This is a conversion method that sometimes detects the current induced in both poles (in the case of a microphone), and in both cases electrostatic force is the basis. For simplicity, an electrostatic speaker will be described as an example. Since the electrostatic force is proportional to the square of the voltage, if it is driven as it is, a driving force with a frequency twice that of the signal is generated. That is, in the case of the signal e, e = e ₀ cos (ωt) → e ² = {e ₀ cos (ωt)} ² = e ₀ ² {1 + cos (2ωt)} / 2, and a driving force of 2ω is generated. To avoid this, add a bias E ₀ to constantly apply electrostatic force (E ₀ >>
e ₀ ) The driving force is (E ₀ + e) ² = E ₀ ² + 2eE ₀ + e ² = E ₀ ² {1 + 2e / E ₀ + (e / E ₀ ) ² } to E ₀ ² {1 + 2e / E ₀ } The frequency component of 2ω can be ignored. It should be noted that the driving force of the ω component is proportional to the electrostatic bias voltage E _{0, though} it is not good enough.

An ultrasonic distance measurement experiment was conducted using the system shown in FIG. Signal frequency is 100kHz (wavelength 3.44mm) and sine wave is 5
First, the ultrasonic wave was emitted from all ultrasonic elements on the transmitting side in the same phase, and the received signal was observed with an oscilloscope using the distance to the object in front as a parameter. As a result, it was clarified that the S / N ratio can be measured even when the object is close to the distance of 10 mm. It is clear that a sufficient effect is obtained as compared with the conventional distance measuring method using the ultrasonic sensor.

Next, a range-finding experiment was performed by fan-shaped scanning of the ultrasonic beam by changing the phase of each ultrasonic element on the transmitting side. ±
In the case of electronic scanning of about 30 degrees, the distance to a near object of about 10 mm could be measured with similar results. Initially,
It was feared that the transmission distance of the ultrasonic beam would be extremely deteriorated due to the decrease of the transmission power by dividing the array type ultrasonic element into transmitting and receiving, but the effect is about 10%,
It was also clarified that the deterioration was offset by the reduction of interference between the transmitting and receiving ultrasonic elements and the improvement of the S / N ratio during reception.

In the above embodiments, the impedance conversion circuit is a MOS type F
We have explained an example that consists of ETs, but in general, MIS type FET
Can be composed of It is also possible to use a junction type FET instead of the MIS type.

〔The invention's effect〕

As described above, when the capacitive array type ultrasonic proximity sensor having the structure of the present invention is used, it is possible to improve the distance measuring performance at a short distance. Also, S /
Since the N ratio is improved, the signal processing after the final waveform synthesis,
That is, even in image processing such as detection of a two-dimensional distance image, processing such as averaging is unnecessary, and the effect of shortening the overall processing time is obtained. In addition, the time and effort required to install a large number of switches during assembly have been saved, and reliability has been improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a capacitive array type ultrasonic proximity sensor according to an embodiment of the present invention, and FIG. 2 shows an impedance conversion circuit provided in the vicinity of an output section of a receiving side ultrasonic element. Fig. 3 is a diagram showing a distance measuring system using the capacitive array type ultrasonic proximity sensor of Figs. 1 and 2, and Fig. 4 is a conventional capacitive array type ultrasonic wave. FIG. 5 is a diagram showing a proximity sensor, and FIG. 5 is a diagram showing a distance measuring system using the capacitive array type ultrasonic proximity sensor of FIG. 102,304 ...... Receiving side ultrasonic element 103,301 …… Sending side ultrasonic element 201 …… First transistor 202 …… Second transistor 302 …… Sending side signal processing circuit 303 …… Signal source 305 …… Impedance conversion circuit 306 …… Reception side signal processing circuit 307 …… Adder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 29/78 H04R 17/00 332 Y

Claims (2)

[Claims] 1. In a capacitive array type ultrasonic proximity sensor capable of transmitting and receiving ultrasonic waves, a part of the capacitive ultrasonic elements forming an array is connected to an output section. A capacitive array type ultrasonic proximity sensor, which is an ultrasonic element dedicated to receiving waves with a built-in source follower circuit, and the remaining ultrasonic elements are dedicated to transmitting waves. 2. The electrostatic capacitance array type ultrasonic proximity sensor according to claim 1, wherein the source follower circuit is composed of a MIS type FET or a junction type FET. Capacitive array type ultrasonic proximity sensor.