JP2006162374A - Capacitance-type object detection sensor and object detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance type object detection sensor and a capacitance-type object detection method for detecting the capacitance between two objects that approach and separate by movement of at least either of them, and detecting at least the distance between the objects or the existence of another object existing between the objects based on the changing capacitance. <P>SOLUTION: This sensor is equipped with an oscillator 2 for oscillating at an oscillation frequency, determined corresponding to the capacitance between the first object 1 which is either of the approaching or separating two objects, and at least the second object X which is the other of the two objects or the third object X between the two objects, a detection part 3 for detecting the change in the oscillation frequency changing following a capacitance change, and a determining part 4 for determining at least the distance between the two objects or the presence of the third object X, based on this detection result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention detects at least one of the capacitance between two objects that move, approach and separate, and based on the changing capacitance, at least the distance between the objects, or between the objects. The present invention relates to a capacitance type object detection sensor for detecting the presence or absence of another object to be detected, and a capacitance type object detection method.

  Various sensors are used for detecting a distance between two objects that are moved and approaching and moving away from each other, and for detecting another object existing between the two objects. For example, an ultrasonic sensor is used as a back sonar that detects the presence and distance of a rear obstacle (another object) and a distance when an automobile is moved backward. In addition, a light sensor in which a light emitting element and a light receiving element are combined is used for an automatic faucet that automatically discharges or stops tap water. In addition, a so-called proximity sensor having a detection distance of about several tens of millimeters employs a high frequency oscillation type, a differential coil type, a magnetic type, and the like, and is mainly used for metal detection. In addition, the capacitive proximity sensor supports not only metal but also non-metal detection.

  For example, Patent Document 1 discloses a technology of a capacitive displacement sensor that measures a displacement of a water surface, a displacement of a vibrating object, and a swinging object as a change in capacitance. In this method, the displacement of the water surface, the vibration object, and the swing object are measured by making the oscillation frequency of the LC oscillator variable by the capacitance (C) detected by the capacitance sensor.

  Patent Document 2 discloses a technique related to a position detection device for a switch that detects an opening / closing operation state of the switch. This constitutes a position detection device using a position detection sensor provided with an LC oscillator that oscillates an output corresponding to the distance to the detected object. By providing unevenness on the detected object side and continuously detecting changes in detection output with respect to the unevenness as stroke curves, it is possible to distinguish between detection / detection and failure.

Japanese Patent Laid-Open No. 2001-4431 (page 2-3, FIG. 1) JP-A-9-89964 (2nd, 5-6 pages, Fig. 1-4)

  The technique described in Patent Document 1 has a detection range of about 20 mm at a relatively short distance (see FIG. 2 of Patent Document 1). Another object of the present invention is to detect a predetermined displacement such as a displacement of a water surface, a vibrating object, or a swinging object. In other words, this is a technique for detecting increase / decrease of an object or a presence position determined in advance within a relatively short range. Therefore, in devices that can be opened and closed (such as doors and windows) that allow people and human body parts to go in and out, improvements such as detection distance can be used for purposes such as detecting the presence of obstacles. Is desired. For example, it can be detected that the device that opens and closes is stopped by an obstacle or the like before the door is completely closed and has not reached a predetermined position. However, it does not support detection of whether an obstacle or the like is present on the way to close the door. Therefore, it cannot be said to be sufficient as a detection device for performing control such as detecting the device that opens and closes before it stops due to an obstacle or the like and feeding it back to the closing operation.

  The technique described in Patent Document 2 is also the same. Although the principle of changing the oscillation frequency of the LC oscillator is used, it can be said that the usage form as a proximity sensor is improved. The output indicating the open / closed state draws a stroke curve as compared with the conventional on / off (see FIG. 4 of Patent Document 2). However, on / off determination is performed using a comparator (see reference numeral 53 in FIG. 1), and the structure of the switch (detected body 61 in FIG. 3) is also limited.

  The present invention has been made in view of the above problems, and detects at least one of the two objects moving and approaching and separating from the object, and based on the changing capacitance, at least the object It is an object of the present invention to provide a capacitance-type object detection sensor and a capacitance-type object detection method for detecting a distance between two objects or the presence or absence of another object existing between the objects.

In order to achieve this object, the characteristic configuration of the capacitive object detection sensor according to the present invention is that it includes the following parts.
That is, depending on the capacitance between the first object that is one of the two objects approaching and separating and the second object that is the other of the two objects or the third object between the two objects. An oscillator that oscillates at a fixed oscillation frequency;
A detection unit that detects a change in the oscillation frequency that changes with a change in the capacitance;
And a determination unit that determines at least the distance between the two objects or the presence or absence of the third object based on the detection result.

  According to this characteristic configuration, the oscillation frequency of the oscillator according to the capacitance detected between the first object and the second object or between the third object and the first object between these two objects. Changes. When the first object and the second object approach or separate from each other, the capacitance between the two objects changes continuously accordingly. The oscillation frequency changes with the change in capacitance. It is possible to know whether the two objects are approaching or separating from each other according to the direction of change of the oscillation frequency (whether it is higher or lower). That is, the approximate distance between both objects can be known. Further, for example, when another object (third object) as an obstacle or the like enters between these two objects, the change in the capacitance is not continuous but abrupt. Therefore, the presence or absence of the third object between the two objects can be determined. As described above, according to this feature configuration, not only the mutual relationship between two objects approaching and separating from each other but also the presence or absence of another object existing between both objects can be detected. A detection sensor can be provided. Of course, the present invention can be applied to either of the two objects, either one of which moves or both of which move.

  Here, the detection unit includes a reference oscillator that oscillates at a reference frequency and a comparison unit that compares outputs of the reference oscillator and the oscillator, and detects a change in the oscillation frequency using the comparison result. This is preferable.

  The capacitance that determines the oscillation frequency of the oscillator changes not only with the distance between objects but also with environmental changes such as ambient temperature changes. Therefore, even if there is no change in the distance between the objects, if the environment such as the temperature changes, the oscillation frequency may also change. Accordingly, it is not preferable that the capacitance type object detection sensor performs erroneous detection. However, if a reference oscillator that oscillates at a reference frequency is provided as in the above characteristic configuration, the oscillation frequency of the reference oscillator also changes in accordance with environmental changes. Further, in the above characteristic configuration, a comparison unit that compares the outputs of the reference oscillator and the oscillator is provided, and a change in the oscillation frequency is detected using the comparison result. If it does in this way, the part by which the oscillation frequency of the reference | standard oscillator and the oscillator was influenced by the environmental change will be canceled by the comparison part. Therefore, it is possible to obtain a capacitance type object detection sensor with enhanced resistance to environmental changes.

  Here, as an example of a preferred embodiment, the reference oscillator may be the same type of oscillator having the same temperature characteristics as the oscillator. As a specific example, the oscillator is an LC oscillator, and the reference oscillator is an LC oscillation type oscillator configured by a capacitor and an inductor having the same temperature characteristics as the oscillator. By making the temperature characteristics the same, it is possible to improve the canceling effect by the comparison unit and to obtain good resistance to environmental changes. Furthermore, it is preferable that the comparison unit includes a mixer that obtains a frequency difference between the reference oscillator and the output of the oscillator. Since the oscillation frequency of the oscillator changes according to the capacitance between the objects, it covers a wide frequency range. Therefore, as described above, it is preferable to provide a mixer for obtaining a frequency difference. By taking the frequency difference from the output of the reference oscillator, it is possible to convert this to a relatively low frequency, especially in the case of a high frequency, and expect improvement in noise resistance and fluctuation error, etc. Can do.

  As another example of the preferred embodiment, the detection unit includes a digital conversion unit that digitizes the reference oscillator and the output of the oscillator, and the comparison unit compares the digitized output with logic. You may provide a calculating part. That is, the comparison process may be performed after the outputs of the reference oscillator and the oscillator are digitized. When the electrostatic capacity type object detection sensor has a digital signal processing device such as a microcomputer, the reference oscillator and the output of the oscillator can be input almost directly. As a result, it is possible to reduce the circuit scale and the time required for determination.

  Furthermore, as another characteristic configuration, the capacitive object detection sensor according to the present invention includes a storage unit that stores a change characteristic according to a distance of the oscillation frequency of the oscillator with respect to the second object and the third object. The determination unit includes a distance between the two objects, a presence / absence of the third object between the two objects, a second object, and a second object based on the detection result of the detection unit and the change characteristic. It is preferable that at least one of the estimation of the types of the three objects and the distance between the first object and the third object be determined.

  According to this characteristic configuration, the capacitance type object detection sensor includes the storage unit that stores the change characteristic of the oscillation frequency of the oscillator with respect to the target object that is the detection target. Then, the determination unit performs the various determinations based on the change characteristics. As a result, the distance between the two objects can be detected based on the actually detected change in oscillation frequency and change characteristics. Further, when another object (third object) exists between these two objects, the presence / absence of the third object can be detected because the change characteristic with respect to the second object and the actual detection result are shifted. Furthermore, when the presence of the third object is detected, the third object is present between the first object and the second object. Therefore, the type (material, etc.) of the third object can be estimated from the approximate distance and change characteristics. Further, from this estimation result, a more accurate distance between the first object and the third object can be detected. Of course, the type of the second object can also be estimated from the approximate distance between the first object and the second object and the change characteristics.

Moreover, the characteristic structure of the capacitance-type object detection method according to the present invention for achieving the above-described object resides in the following steps.
That is, a static object between a first object that is one of the two objects approaching and separating and a second object that is the other of the two objects or a third object between the two objects. A capacitance detection step for detecting capacitance;
A frequency change detecting step of detecting a change in the oscillation frequency that changes with a change in the capacitance of an oscillator that oscillates at an oscillation frequency determined according to the capacitance;
The distance between the two objects, the presence / absence of the third object, the third object, based on the change characteristics corresponding to the distance of the oscillation frequency with respect to the object stored in advance and the result of the frequency change detection step A determination step of determining at least one of the estimation of the type of the object and the distance between the first object and the third object.

  Here, the frequency change detection step preferably includes a comparison step of comparing the output of the reference oscillator that oscillates at a reference frequency and the oscillator, and it is preferable to detect a change in the oscillation frequency using the comparison result. .

  By performing the above steps, it is possible to obtain the same effect as that of the electrostatic capacitance type object detection sensor.

  Here, it is preferable that the determination step is determined based on a slope of change of the detected oscillation frequency with respect to time.

  The change characteristic is different depending on the object. Therefore, the change characteristics with respect to the passage of time, such as the time when the objects (first object and target object (second object and third object)) approach each other, are different for each target object. The slope of the change characteristic is also different for each object. Therefore, when the determination is made based on the detected change in the oscillation frequency as in the above-described method, good object detection can be performed. The same applies to change characteristics with respect to changes in the distance between objects. That is, when there is a change in distance, it naturally takes time, so a good determination can be made based on the slope of the change characteristic.

  Further, in the determination step, a change in the oscillation frequency is detected based on a change amount or a change gradient with respect to time of the oscillation frequency detected by the frequency change detection step and a predetermined first reference value. It is preferable to determine that this is due to environmental changes.

  In the case where the comparison step is not provided, of course, even if the comparison step is provided, the oscillation frequency may change with time due to a change in ambient temperature or the like. However, such a change usually does not occur abruptly but occurs over a relatively long time. On the other hand, a reduction in the distance between the objects due to the movement of the object and a change in the oscillation frequency due to the appearance of the object occur more rapidly than the environmental change, and generally the amount of change and the slope of the change are large. Therefore, for example, when the amount of change or the slope of the change is small with respect to a predetermined first reference value, it can be considered that the change is gentle. In such a case, if this is determined to be due to an environmental change, the effect of preventing erroneous detection can be obtained.

  Further, it is preferable that the determination step determines the presence or absence of the third object based on the change amount or the slope of the change and a second reference value larger than the first reference value. is there.

  According to this method, the second reference value larger than the first reference value is set. Then, based on the second reference value, it is determined whether or not the oscillation frequency has changed abruptly with respect to the gentle change due to the environmental change or the change due to the shortening of the distance between objects. This can be determined, for example, based on whether or not the amount of change or the slope of change has changed beyond the second reference value. If there is a sudden change, it is determined that a third object exists between the two objects approaching and separating. As a result, a quick determination is possible. For example, even when a third object suddenly enters between the two objects as an obstacle, this can be detected at an early stage.

  Moreover, when the speed at which the plurality of objects approach is known, it is preferable that the determination step determines the type of the object based on the change characteristics with respect to the plurality of types of the object.

  According to this characteristic configuration, it is possible to determine what the object is based on the change characteristics with respect to the plurality of objects. For example, it can be used for purposes such as which paper is being fed to a printer that can print on recording media (paper) of different materials.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the capacitive object detection sensor according to the present invention includes an antenna 1, an LC oscillator 2 (corresponding to the oscillator according to the present invention), a detection unit 3, and a determination unit 4. Configured. Here, the antenna 1 is provided on one side (corresponding to a first object of the present invention) of two objects approaching and separating. Then, the distance to the object X or the like is determined based on the capacitance that changes due to the variation in the distance between the first object and the object X (corresponding to the second object or the third object of the present invention). The LC oscillator 2 oscillates at an oscillation frequency determined according to an inductor element and a capacitor element included in the oscillation circuit, an inductance component of the antenna 1, and a capacitance between the antenna 1 and the object X. The capacitance between the antenna 1 and the object X changes due to a change in the distance between the first object provided with the antenna 1 and the object X. Therefore, the oscillation frequency of the LC oscillator 2 is practically determined by the capacitance between the antenna 1 and the object X. The detection unit 3 detects a change in the oscillation frequency of the LC oscillator 2 that is determined along with the change in capacitance. In this embodiment, an LC oscillator is used as the oscillator. However, the present invention is not limited to this as long as the oscillator can be configured so that the oscillation frequency changes depending on the capacitance.

  Here, the two objects approaching and separating are, for example, the door frame and door of a sliding door of an automobile as shown in FIG. 7, or the opening / closing portion of a device that opens and closes such as a window frame and window glass. The composition corresponds. In the example shown in FIG. 7, the door and the window glass are the first objects, and the antenna 1 is provided at the end that is the joint portion when opening and closing. Similarly, as shown in FIG. 8, the door frame and door of the hatchback door of the automobile also correspond to a plurality of objects, and the antenna 1 is provided at the end of the door corresponding to the first object. The antenna 1 may be provided on the door frame or window frame side. In this case, the door frame or window frame side is the first object. Therefore, the one that is not the first object among the doors, door frames, window glass, and window frames corresponding to each other corresponds to the second object.

  Also, when opening and closing doors and windows, especially when closing, when clothes or umbrellas or other obstacles are sandwiched between the door frame and the door and between the window frame and the window, The umbrella corresponds to the third object between the two objects. In other words, there is a correspondence relationship between the first object (for example, door, window glass) and the second object (for example, door frame, window frame) as a third object (for example, clothing) that exists as an object. Hereinafter, the embodiment of the present invention will be described by taking this correspondence as an example.

As shown in FIG. 1, the electrostatic capacitance between the object 1 as the window frame (second object) is detected by the antenna 1 provided on the window glass (first object) (the electrostatic capacity of the present invention). This corresponds to the capacity detection step.) The LC oscillator 2 oscillates at an oscillation frequency determined according to the detected capacitance. The closer the distance between the window glass and the window frame, that is, the distance between the antenna 1 and the object X, the greater the capacitance. That is, when the capacitance is C, the dielectric coefficient of the object X is a, the dielectric constant of the space (for example, air) between the antenna 1 and the object X is ε, the distance is l, and the coupling area is S, It becomes a relationship like this.
C = (a · ε · S) / l (Equation 1)

Further, the oscillation frequency f of the LC oscillator 2 is expressed by the following equation, where L is the inductance of the LC oscillator 2 (^ indicates a power).
f = 1 / (2π · (L · C) ^ (1/2)) (Equation 2)

  As shown in [Expression 1] and [Expression 2], the capacitance and the oscillation frequency of the LC oscillator 2 change according to the distance between the first object and the second object. This change in oscillation frequency is detected by the detection unit 3 (corresponding to the frequency change detection step of the present invention). Based on this detection result, the determination unit 4 determines at least the distance to the second object or the presence and distance of the third object existing between the second object (corresponding to the determination step of the present invention). To do.) The configuration and method for detecting and determining this change in oscillation frequency will be described below.

  As shown in FIG. 2, the detection unit 3 includes a reference oscillator 6 that oscillates at a reference frequency, and a comparison unit 7 that compares outputs of the reference oscillator 6 and the LC oscillator 2. The capacitance C changes not only with changes in the distance between objects, but also with environmental changes such as changes in ambient temperature. Therefore, even if there is no change in the distance between the objects, if the environment such as the temperature changes, the oscillation frequency may also change. If this change is detected as a change in distance, the determination unit 4 may make an erroneous determination, which is not preferable. However, if the oscillation frequencies of the LC oscillator 2 and the reference oscillator 6 are compared, it is possible to cancel a portion that has been affected by an environmental change. As a result, resistance to environmental changes can be improved.

  The reference oscillator 6 is an LC oscillation type oscillator composed of a capacitor and an inductor having the same temperature characteristics as the LC oscillator 2. By making the temperature characteristics the same, the effect of cancellation by the comparison unit 7 is enhanced, and resistance to environmental changes can be obtained well.

  And as one Embodiment which comprises this comparison part 7, there exists a thing as shown in FIG. As shown in the figure, a mixer 8 for obtaining a difference in frequency between the outputs of the reference oscillator 6 and the LC oscillator 2 and a filter circuit 9 for extracting only a necessary frequency from the output of the mixer 8 are provided. The oscillation frequency of the LC oscillator 2 that changes as the capacitance changes according to the distance between the object X and the antenna 1 covers a wide frequency range. Thus, when the frequency difference is obtained by the mixer 8, it can be converted to a relatively low frequency particularly in the case of a high frequency. As a result, since signal processing can be performed at a low frequency, noise resistance and fluctuation error can be improved. The filter circuit 9 is a low-pass filter (LPF) in this embodiment. It is suitable for extracting only the difference information with a reduced frequency. The output of the filter circuit 9 is processed by a post-processing circuit 10 such as an operational amplifier or a comparator, and the detection result is transmitted to the determination unit 4. The process in the comparison unit 7 corresponds to the comparison process of the present invention.

  Moreover, as another embodiment which comprises this comparison part 7, there exists a thing as shown in FIG. In this embodiment, a microcomputer (hereinafter referred to as a microcomputer) 13 is used, and the function of the determination unit 4 and a part of the function of the detection unit 3 are realized by the microcomputer 13. The detection unit 3 includes a digital conversion unit 11 that digitizes the outputs of the reference oscillator 6 and the LC oscillator 2. The digital conversion unit 11 includes a comparator, and includes a digital conversion unit 11 b that handles the reference oscillator 6 and a digital conversion unit 11 a that handles the LC oscillator 2. The comparison unit 7 includes a logical operation unit 12 that compares these digitized outputs, and detects a change in the oscillation frequency by the logical operation. The processing in the comparison unit 7 according to the present embodiment also corresponds to the comparison process of the present invention.

  Based on the configuration described above, a change in the oscillation frequency is detected, and the determination unit 4 performs various determinations as described below. For example, the distance between the first object (antenna 1) and the second object (object X), the presence or absence of the third object (object X) existing between the first object and the second object (object X), the second For example, the type of the object or the third object, the distance from the third object, and the like. Any one of these determinations or a plurality of determinations may be determined. That is, if the third object enters between the first object and the second object while determining the distance between the first object (antenna 1) and the second object (object X), this first The presence or absence of three objects is determined. Further, the third object that has entered becomes the object X instead of the second object, and detects the distance between the first object (antenna 1) and the third object (object X). When applied to the sliding door shown in FIG. 7, when the door is closing toward the door frame, the distance between the door and the door frame is determined, and the entry of clothes or the like is detected along the way. can do.

  In order to perform such various determinations, as shown in FIG. 5, a storage unit 5 is provided that stores a change characteristic according to the distance of the oscillation frequency of the LC oscillator 2 with respect to a plurality of objects (objects) in advance. Yes. Then, the determination unit 4 performs the above-described various determinations based on the detection results detected by the detection unit 3 and the change characteristics stored in the storage unit 5. Here, the change characteristics are as shown in FIG. 6 and indicate the correlation between distance and frequency or frequency difference (variation). As shown in FIG. 6, the object A and the object B show different characteristics. The determination unit 4 determines the distance to the object X (target object), whether it is the object A or the object B, and the like based on the difference in characteristics. Although two types of characteristics are shown in FIG. 6, if a large number of these are prepared, more accurate determination can be performed. Further, the difference in characteristics between the object A and the object B can depend on various viewpoints such as a difference in what frequency at which distance and a difference due to the slopes S1 and S2 of the characteristic curve. Such various determinations by the determination unit 5 correspond to determination steps of the present invention.

  The determination based on the frequency difference is, for example, as follows. For example, when the distance between two objects decreases, the oscillation frequency changes continuously. In particular, in a switchgear or the like that operates at a constant speed, the movement time and the movement distance can be predicted in advance, and the detection point may be determined accordingly. The change characteristics stored in the storage unit need only be prepared with points corresponding to this, and the limited storage area of the storage unit can be used effectively.

  The determination based on the slope of the characteristic curve is, for example, as follows. The change characteristic slope S1 of the object A shown in FIG. 6 is larger than the change characteristic S2 of the object B. When the slope of the change curve of the oscillation frequency detected by the detection unit 3 is S1, for example, it can be determined as follows. That is, it can be determined that the object A is a metal and the door (first object) provided with the antenna 1 is approaching (closing operation) toward the door frame (second object). When the slope of the change curve of the oscillation frequency detected by the detector 3 is S2, it can be determined as follows. That is, the door (first object) should be closing toward the door frame (second object), but if it is approaching toward a cloth (object B: third object) such as clothes. Can be judged. As a result, it is also possible to perform control to prevent clothes and the like from being caught. As described above, in the determination step, the determination can be made based on the detected inclination of the change in the oscillation frequency.

  In the above embodiment, the amount of change in the oscillation frequency and the slope of the change are detected based on the measurement results measured every predetermined period or every predetermined moving distance. For example, every predetermined time is to measure every several milliseconds. For each predetermined moving distance, when the operation speed is known, such as a power window or a power sliding door of an automobile, for example, measurement is performed every time it moves several tens of mm. Although FIG. 6 shows a change characteristic with respect to a change in the distance between objects, a change characteristic with respect to time may be used. That is, when a change in the distance is accompanied, the passage of time is naturally accompanied and the same can be considered. Conversely, the object may not be moved over time, but in this case, if the presence or absence of the object movement is known, the following determination can be performed.

  That is, the determination unit 4 determines whether or not the amount of change or inclination of change with time of the oscillation frequency is smaller than a predetermined reference value (corresponding to the first reference value of the present invention). . Then, based on the determination result, it is determined that the change in the oscillation frequency is due to the environmental change. For example, in the embodiment described with reference to FIGS. 2 to 4, the configuration and method of providing the reference oscillator 6 are shown in order to suppress the influence on the detection result due to the environmental change. The discriminating step is particularly useful when such a configuration and method are not employed because the influence that cannot be suppressed by such a configuration and method and the influence of environmental changes are small.

  When the oscillation frequency changes with the passage of time due to environmental changes, such a change does not occur abruptly but takes a relatively long time. On the other hand, shortening of the distance between objects due to the movement of the object and change in the oscillation frequency due to the appearance of the object occur more rapidly than changes in the environment. Therefore, when the change amount is moderate with respect to a predetermined change amount as in the above method, if it is determined that the change amount is due to an environmental change, the possibility of preventing erroneous detection is increased.

  When it is determined that the change in the oscillation frequency is due to an environmental change, the determination is made based on the change characteristics matched to the oscillation frequency after the change. That is, the error determined to be caused by the environmental change is used as correction information for the change characteristic stored in the storage unit 5. Then, the subsequent processing (determination) is performed based on the corrected change characteristic. If correction is not performed, there is a possibility that it will be determined as a large change at a certain point in time due to the accumulation of gradual changes. However, when the above is performed, erroneous determination due to error accumulation can be prevented.

  Further, the determination unit 4 determines whether or not the amount of change in the oscillation frequency or the slope of the change is greater than the second reference value that is greater than the first reference value (second determination step). And based on this discrimination | determination result, the presence or absence of a 3rd object is determined. For example, it is assumed that the door (first object) including the antenna 1 is approaching (closing operation) toward the metal door frame (second object). Here, it can be detected that clothes (third object) have entered between the two objects. In the closing operation / opening operation, when the first object and the second object approach or separate from each other, a change in the oscillation frequency according to a change characteristic with respect to time or relative distance is detected. However, when clothes (third object) appear between the first object and the second object, a deviation that does not match the change characteristics of the metal is detected. Therefore, a second reference value corresponding to this deviation is set, and if it exceeds this value, the presence of the third object is determined as a sudden change.

  The frequency at this time can be measured by counting the leading edge or trailing edge within a predetermined time of the oscillation waveform of the oscillator 2 or the output waveform of the comparison unit 7. That is, since the number of cycles within a predetermined time is measured, the frequency is measured. In such a case, a change in frequency can be detected using the counting result itself. In the present embodiment, a binary counter is used for counting by an electronic circuit. In binary counting, a magnification indicated by a power of 2 such as 2 times, 4 times, or 8 times can be easily obtained by carry. Therefore, when one of the counting results of a certain time zone and another time zone has a carry and the other does not, a magnification corresponding to the carry is generated. Therefore, it is possible to easily detect whether or not the oscillation frequency has changed rapidly based on this magnification.

  Alternatively, a method may be used in which a group for each frequency band is created and a group to which a frequency measured in a predetermined unit time belongs is detected. When the group of the frequency band detected in this way moves, for example, two groups within a determination period defined by several predetermined unit times, it is determined that a sudden change has occurred. Also good.

  In the above, FIG. 6 shows two types of change characteristics, and it has been described that the material of the object X (target object) can be estimated to determine what this is. Then, it has been explained that more accurate determination can be made if a large number of such change characteristics are prepared. In particular, when the speed at which the objects approach each other is known, the type of the object can be specified based on the change characteristics with respect to the plurality of objects.

  For example, the frequency (or frequency difference) of the object A and the object B is the same value at the distance (position or time) indicated by the symbol T1 shown in FIG. However, the frequencies of the object A and the object B have different values at the distance of the code T2 that is a little closer to the antenna. Furthermore, the frequency difference between the object A and the object B becomes large at the distance of the code T3 that is close to the antenna. At the distance of the code T4 that is closer than the code T3, the difference between the two frequencies becomes very large. Thus, if the distance between the two is known (or predictable) in advance, it can be well derived which object the change characteristic corresponds to from the frequency according to the distance (symbols T1 to T4, etc.). . As a result, it is possible to specify the type of the object. In addition, if discrimination is made from the detection results at several points instead of just one point, discrimination with higher accuracy becomes possible.

  For example, when the operation speed is known, such as a power slide door or power window of an automobile, whether the destination of the door or window glass is a door frame, window frame, clothes, or other obstacle Can be determined. Some welfare vehicles have a mechanism that causes the vehicle seat to swing out of the vehicle, and the swing-out state can also be determined. Then, feedback can be applied to control the power slide door and the power window according to the determination result.

  As another application example of the present invention, it is possible to determine which paper is being fed by a printer or the like capable of printing on recording media (paper) of different materials. By feeding back the result, it is possible to perform control such that image processing and printing processing suitable for each sheet are performed.

  The present invention can be applied to an object detection sensor for detecting an open / closed state of a device to be opened / closed, an open / closed state monitoring device using the same, a pinch detection device, and the like. The opening / closing device can be applied to, for example, a power window, a power slide door, a back door of an automobile, an automatic door such as a building or a railway, a revolving door, and the like. Further, it can be applied as a paper detection device in a paper transport mechanism such as a printer.

The block diagram which shows embodiment of the electrostatic capacitance type object detection sensor which concerns on this invention The block diagram which shows the structural example of the detection part of FIG. The block diagram which shows the example of 1 structure of the comparison part of FIG. The block diagram which shows the other structural example of the comparison part of FIG. The block diagram which shows other embodiment of the electrostatic capacitance type object detection sensor which concerns on this invention. The graph which shows the example of the change characteristic which the memory | storage part of FIG. 5 memorize | stores Schematic diagram showing an installation example of the antenna of FIGS. Schematic diagram showing an installation example of the antenna of FIGS.

Explanation of symbols

1 Antenna (first object)
2 LC oscillator 3 Detection unit 4 Determination unit X Object (object, second object, third object)

Claims (9)

Oscillation determined according to the capacitance between a first object that is one of the two objects approaching and separating from each other and a second object that is the other of the two objects or a third object between the two objects An oscillator that oscillates at a frequency;
A detection unit that detects a change in the oscillation frequency that changes with a change in the capacitance;
A determination unit that determines the distance between at least the two objects based on the detection result or the presence or absence of the third object;
A capacitive object detection sensor comprising:   The detection unit includes a reference oscillator that oscillates at a reference frequency, and a comparison unit that compares outputs of the reference oscillator and the oscillator, and detects a change in the oscillation frequency using the comparison result. 2. The electrostatic capacitance type object detection sensor according to 1.   The storage unit stores a change characteristic according to a distance of the oscillation frequency of the oscillator with respect to the second object and the third object, and the determination unit is based on a detection result of the detection unit and the change characteristic. , The distance between the two objects, the presence or absence of the third object between the two objects, the estimation of the type of the second object and the third object, the distance between the first object and the third object The electrostatic capacitance type object detection sensor according to claim 1 or 2 which judges at least any one. Capacitance between a first object that is one of the two objects approaching and separating and a second object that is the other of the two objects or a third object between the two objects. A capacitance detection step of detecting
A frequency change detecting step of detecting a change in the oscillation frequency that changes with a change in the capacitance of an oscillator that oscillates at an oscillation frequency determined according to the capacitance;
The distance between the two objects, the presence / absence of the third object, the third object, the third object based on the change characteristic according to the distance of the oscillation frequency with respect to the object stored in advance and the result of the frequency change detection step A capacitance type object detection method comprising: an object type estimation; and a determination step of determining at least one of the distance between the first object and the third object.   5. The frequency change detection step includes a comparison step of comparing a reference oscillator that oscillates at a reference frequency with an output of the oscillator, and detecting a change in the oscillation frequency using the comparison result. The electrostatic capacitance type object detection method as described.   The capacitance type object detection method according to claim 4 or 5, wherein the determination step is performed based on a slope of a change of the detected oscillation frequency with respect to time.   In the determination step, the change in the oscillation frequency is changed in the environment based on the change amount or the inclination of the change with respect to time of the oscillation frequency detected by the frequency change detection step and a predetermined first reference value. The electrostatic capacity type object detection method according to any one of claims 4 to 6 which judges that it is based on.   The electrostatic capacity according to claim 7, wherein the determination step determines the presence or absence of the third object based on the change amount or the gradient of the change and a second reference value larger than the first reference value. Capacitive object detection method. The determination step determines the type of the object based on the change characteristics with respect to the plurality of types of the object when the speed at which the plurality of objects approach is known. The capacitance-type object detection method according to the item.

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