JP5010156B2 - Proximity sensor - Google Patents

Description

  The present invention relates to a proximity sensor.

Conventionally, proximity sensors that detect an object to be detected based on a change in oscillation amplitude of an oscillation circuit including a coil are known.
In this type, for example, the oscillation amplitude decreases as the proximity sensor is brought closer to the object to be detected, and the object to be detected is detected when the oscillation amplitude falls below a preset detection threshold. The detection of an object is judged.
Japanese Patent Publication No. 5-48646

By the way, there is a case where the user wants to perform not only detection of the presence / absence of the detected object but also stable detection of whether the detected object is detected with stable accuracy.
As such stability detection, for example, as shown in FIG. 7A, when a value slightly smaller than the detection threshold is set as the stability detection threshold and the oscillation amplitude becomes equal to or less than the stability detection threshold, the object to be detected is detected. It is conceivable to determine that the detection is performed with stable accuracy.

However, when performing stable detection by such a method, stable detection is possible when the oscillation amplitude changes slowly (so-called soft oscillation method). However, as shown in FIG. If the oscillation amplitude fluctuates greatly in the vicinity (so-called hard oscillation method), the oscillation amplitude falls below the detection threshold and immediately falls below the stability detection threshold. Is difficult.
The present invention has been completed based on the above situation, and provides a proximity sensor capable of detecting the stable detection state of an object to be detected even when the oscillation amplitude varies greatly. For the purpose.

As a means for achieving the above object, the proximity sensor of the invention of claim 1 includes an oscillation circuit whose oscillation amplitude changes in a hard oscillation mode according to the distance to the object to be detected;
Detecting means for detecting the object to be detected based on a comparison result between an oscillation amplitude of the oscillation circuit and a predetermined detection threshold ;
A feedback circuit for supplying a feedback current for maintaining a predetermined oscillation amplitude in the oscillation circuit ,
The feedback circuit is
A comparison circuit that outputs a pulse signal based on a comparison result between the oscillation threshold and the sustaining threshold lower than the detection threshold;
A feedback current supply circuit that supplies the feedback current according to a pulse signal output from the comparison circuit,
Stability detection means for detecting a stable detection state of the detected object by the detection means, assuming that the amount of the feedback current is equal to or higher than a reference level when the duty of the pulse signal output from the comparison circuit is equal to or greater than a predetermined value ; ,
It is characterized by comprising a notification means for notifying that the stability detection state has been detected by the stability detection means.
The hard oscillation method is a method in which the fluctuation of the oscillation amplitude is larger than that of the soft oscillation method, and is generally a method in which the oscillation amplitude changes greatly in the vicinity of the distance where the detection object is detected by the detection means. The soft oscillation method is a method in which the oscillation amplitude changes more slowly than the hard oscillation method.

Invention of Claim 2 is provided with the display means which can be visually recognized in the thing of Claim 1 ,
The notification means is characterized in that the display means notifies that the stability detection state has been detected.

The invention of claim 3 is characterized in that in the apparatus of claim 1 or 2 , the apparatus further comprises setting means capable of setting and changing the reference level for detecting the stability detection state by the stability detection means. Have.

<Invention of Claim 1>
By adopting a configuration using an oscillation circuit using a hard oscillation method, compared to a configuration using an oscillation circuit using a soft oscillation method in which the change in oscillation amplitude relative to the object to be detected is relatively gentle, the detection means The influence of noise at the time of detection can be reduced.
However, in such a configuration (hard oscillation method), the stable detection state of the detected object based on the oscillation amplitude at the position on the detected object side relative to the position where the detected object is detected by the detecting means Is difficult to detect because the change in oscillation amplitude is large.
On the other hand, according to this configuration, when the amount of feedback current for maintaining a predetermined oscillation amplitude is equal to or higher than the reference level, the stability detection state is detected by the stability detection unit.
Therefore, unlike the configuration in which the stable detection state is detected based on the oscillation amplitude in the same manner as the detection by the detection means, the oscillation amplitude varies greatly as in the oscillation circuit using the hard oscillation method. Even if it is difficult to perform stability detection, it is possible to detect the stability detection state of the object to be detected.
In addition, if the oscillation state is stopped according to the distance to the object to be detected, there is a possibility that a rise delay time during oscillation may occur, which is not desirable. On the other hand, according to this configuration, even when the oscillation state is at a distance where the oscillation state is stopped, if the oscillation state is maintained by supplying the feedback current, it is possible to reduce the delay time of rising at the time of oscillation.
The stability detecting means detects the stability detection state of the object to be detected, assuming that the amount of the feedback current is equal to or higher than a reference level when the duty of the pulse signal output from the comparison circuit is equal to or higher than a predetermined value. Therefore, the configuration of the feedback circuit used for sustaining the oscillation state can be used for detection of the stable detection state, and the stable detection state can be detected with a simple configuration.

<Invention of Claim 2 >
According to this configuration, it becomes possible for the user to visually recognize whether or not the detected object is stably detected.

<Invention of Claim 3 >
According to this configuration, it is possible to change the setting to an appropriate reference level for performing detection by the stability detection unit in accordance with the detection environment or the like.

An embodiment of a proximity sensor according to the present invention will be described with reference to FIGS. The proximity sensor of this embodiment is configured such that a feedback current is supplied so that the oscillation amplitude of the oscillation circuit 10 can be maintained at a predetermined magnitude.
1. Electrical Configuration of Proximity Sensor As shown in FIG. 1, the proximity sensor 1 according to the present embodiment employs a hard oscillation method (see FIG. 3) as a configuration for detecting the presence or absence of the object W to be detected. Circuit 10, integrating circuit 20 that integrates the oscillation amplitude of oscillation circuit 10, and the level of the integrated signal integrated by integrating circuit 20 is compared with a predetermined detection threshold value Dth, and a comparison for detection that outputs the comparison result Circuit 30 (corresponding to “detection means” of the present invention). Further, as a configuration for supplying a feedback current for maintaining the oscillation amplitude to the oscillation circuit 10, the comparison circuit 40 for sustaining that compares the signal level integrated by the integration circuit 20 with a predetermined sustaining threshold Cth (this book) And a sustain feedback current Ic (corresponding to the “feedback current” of the present invention) for maintaining (sustaining) the oscillation amplitude based on the comparison result from the sustain comparison circuit 40. A feedback control circuit 60 for controlling. Further, a CPU 50 (corresponding to the “stability detection means” of the present invention) that detects whether the detection result W is stably detected when a comparison result signal from the sustain comparison circuit 40 is input, and detection The display unit 70 (corresponding to the “display unit, notifying unit” of the present invention) in which the result is displayed so as to be visible, the output circuit 80 for outputting the detection result to an external device (not shown), and the stable detection state by the CPU 50 An operation unit 51 (corresponding to the “setting unit” of the present invention) that allows the user to change the setting of a reference level for detection is provided.

  As shown in FIG. 2, the oscillation circuit 10 includes an LC resonance circuit 11 including a detection coil L and a capacitor C connected in parallel with the detection coil L. A current is supplied to the LC resonance circuit 11 from the constant current source 2 via the power source 3, and the power source 3 is connected to the base of the NPN transistor 4 so that the current is amplified by the NPN transistor 4. .

  The emitter of the NPN transistor 4 is grounded via a variable resistor 5 that determines the collector current, and the collector of the NPN transistor 4 is connected to the current mirror circuit CM1.

  The current mirror circuit CM1 is formed by PNP transistors 21, 22, and 23, and the collector of the NPN transistor 4 is connected to the base-collector common connection terminal of the PNP transistor 21.

  The current value obtained from the LC resonance circuit 11 is amplified by the NPN transistor 4, and the current value identical to the collector current is fed back to the LC resonance circuit 11 through the transistor 22 by the current mirror circuit CM 1. Since positive current feedback is applied in this way, oscillation is performed at the resonance frequency of the LC resonance circuit 11.

  Further, in the present embodiment, even when the object W is close to the proximity sensor (when the oscillation amplitude suddenly decreases), when the distance is within a predetermined range (amplitude duration range), the predetermined magnitude A feedback current supply circuit 25 (a portion indicated by a two-dot chain line in FIG. 2) for supplying a feedback current (sustained feedback current Ic) is provided so as to maintain the oscillation amplitude of the length (sustained threshold Cth).

The feedback current supply circuit 25 includes transistors 13 to 15 and 23.
Specifically, the collector of the PNP transistor 23 is connected to the collector-base common connection end of the NPN transistor 13. The NPN transistor 13 and the NPN transistor 14 form a current mirror circuit CM2, and the collector of the other NPN transistor 14 is connected to the base-collector common connection end of the multicollector transistor 15. The other collector terminal of the multi-collector transistor 15 is connected in series to the LC resonance circuit 11. The base and collector of the NPN transistor 13 are connected to the collector terminal of the switching transistor 16. The switching transistor 16 is switched on and off by a pulse signal from the feedback control circuit 60. The operation of the current mirror circuit CM2 is controlled by this switching, and the continuous feedback current supplied to the LC resonance circuit 11 is controlled. Ic is controlled.

The integrating circuit 20 integrates the oscillation amplitude signal to output an integrated signal having a level corresponding to the distance to the detection target W as shown in FIG.
The detection comparison circuit 30 compares the level of the integration signal output from the integration circuit 20 with a predetermined detection threshold value Dth, and if the level of the integration signal is equal to or lower than the detection threshold value Dth, If the high level indicating that the object W has been detected and the level of the integrated signal is greater than the detection threshold Dth, a pulse signal (digital signal) that indicates a low level indicating that the object W has not been detected is displayed. To the unit 70 and the output circuit 80.

  As shown in FIG. 5, the sustain comparison circuit 40 compares the level of the integration signal output from the integration circuit 20 with a predetermined sustain threshold Cth, and the level of the integration signal is the sustain threshold Cth. If it is less than or equal to the high level for increasing the continuous feedback current Ic and the level of the integrated signal is greater than the detection threshold Dth, the low level for temporarily stopping the increase of the continuous feedback current Ic A pulse signal (digital signal) is output to the CPU 50 and the feedback control circuit 60. As a result, within a predetermined range (amplitude sustaining range) on the detected object W side with respect to the detection position X, the oscillation amplitude does not become zero, and the predetermined oscillation amplitude is maintained.

Here, since the oscillation amplitude in the LC resonance circuit 11 is reduced by the loss based on the eddy current generated in the detection target W, in order to maintain a constant oscillation amplitude, the distance to the detection target is short. As the oscillation amplitude decreases, the time during which the pulse signal output from the sustain comparison circuit 40 is at a high level is lengthened.
Therefore, as shown in FIG. 3, the sustain feedback current Ic supplied to the LC resonance circuit 11 increases as the distance to the object to be detected becomes shorter in the amplitude sustain range (between X and C). .

  The CPU 50 performs the detection of the detection object W in a stable state depending on whether the duty (ratio between the high level time and the low level time) of the pulse signal output from the sustain comparison circuit 40 is a predetermined value or more. It is designed to detect whether or not As a result, the stable detection state is detected when the current amount of the continuous feedback current Ic is equal to or higher than the reference level. The “current amount of the sustaining feedback current Ic” here is not an instantaneous current amount when the pulse signal is at a high level, but a unit time determined by repetition of the high level and low level of the pulse signal ( It is the amount of current (predetermined time) (average value of the amount of current).

  Specifically, the duty (ratio between the high level time and the low level time) is obtained from the pulse signal output from the sustain comparison circuit 40, and this duty is set to a predetermined value M (for example, as shown in FIG. 4). When the stable detection position Y is determined, the current amount of the secondary feedback current Ic is determined to be greater than or equal to the reference level when the 20% duty at the position is greater than or equal to the predetermined value M). It is determined that the detection of W is performed in a stable state (in a stable detection state), and such information is output to the display unit 70 and the output circuit 80. The predetermined value M is configured to be changeable by designating a desired duty (0 to 100%) on the operation unit (not shown). In this case, a desired position can be set as the stable detection position.

  The display unit 70 receives the outputs from the detection comparison circuit 30 and the CPU 50 (stability detection means) and displays the information on the detection (stability detection) result so that the user can recognize it.

  The output circuit 80 outputs the detection results in the detection comparison circuit 30 and the CPU 50 (stability detection means) to an external device such as a PC.

  Based on the pulse signal from the sustain comparison circuit 40, the feedback control circuit 60 converts the pulse width into a pulse width that can maintain the oscillation amplitude at a predetermined level (sustain threshold Cth) and outputs the pulse width. The pulse signal output from the feedback control circuit 60 is supplied to the base of the switching transistor 16 shown in FIG. Thereby, even when the proximity sensor 1 approaches the detection target W for a predetermined distance or more, the oscillation amplitude does not become zero, and the oscillation amplitude of a predetermined level is maintained.

2. The operation at the time of detection by the proximity sensor will be described.
When the oscillation circuit 10 continues to oscillate, when the metal detection object W approaches the detection coil L, the conductance changes, so the oscillation amplitude decreases. When approaching the vicinity of the detection position X, the oscillation amplitude sharply decreases due to the characteristics of the oscillation circuit 10 using the hard oscillation method, so that the integration signal level of the integration circuit 20 also rapidly decreases.

  At this time, the integration signal level is compared with the detection threshold value Dth by the detection comparison circuit 30, and when the integration signal level falls below the detection threshold value Dth at the detection position X, a high level signal is output.

  Next, in order to maintain the rapidly decreasing oscillation amplitude at the predetermined sustain threshold Cth, the feedback circuit (sustain comparison circuit 40, feedback control circuit 60, transistor 16, feedback current supply circuit 25) is used. By supplying the continuous feedback current Ic to the oscillation circuit 10, even when the detection target W approaches, a predetermined oscillation amplitude is maintained up to a predetermined distance. As a result, the delay time when the oscillation amplitude rises when the detection target W is separated from the detection position again is reduced.

  Here, as shown in FIG. 3, the continuous feedback current Ic increases at a predetermined rate as it approaches the object W to be detected. The sustain feedback current Ic changes according to the duty of the pulse signal output from the sustain comparison circuit 40.

  Therefore, when the detected object W further approaches and reaches the stable detection position Y, the CPU 50 reaches the stable detection position Y by the duty of the pulse signal output from the sustain comparison circuit 40 at that time (see FIG. 4). This is detected, the stability detection state is detected, and information of the detection result concerning the display unit 70 and the output circuit 80 is output. Thereby, the stability detection information is displayed on the display unit 70, and the user is notified that the stability detection is being performed.

3. CPU Processing Next, CPU processing will be described. The stability detection process is repeatedly performed to determine whether the detection of the detection object is stably performed.

<Stability detection processing>
As shown in FIG. 6, the CPU 50 obtains the high level time and the low level time of the pulse signal from the sustain comparison circuit 40, and calculates the duty that is the ratio (ratio) of the low level time to the high level time. (S11).

Next, the CPU 50 determines whether or not the calculated duty is equal to or greater than M stored in advance in a memory (not shown) (S12).
When it is determined that the duty is smaller than M (“N” in S12), the stability detection process ends.

  On the other hand, when it is determined that the duty is M or more (“Y” in S12), information indicating that the detection state is stable is output to the display unit 70 and the output circuit 80 (S13).

  Thereby, information that the detection state of the detection target W is stable (in a stable detection state) is displayed on the display unit 70, and the user can recognize the information.

4). Advantages of the present embodiment (1) According to the present embodiment, since the oscillation circuit 10 using the hard oscillation method is used, the soft oscillation method in which the change in the oscillation amplitude with respect to the detected object W is relatively gentle. Compared with the configuration using the oscillation circuit 10 in which is used, the influence of noise at the time of detection by the detection comparison circuit 30 (detection means) can be reduced.
However, in such a configuration, the stable detection state of the detection target W is detected based on the oscillation amplitude at a position near the distance where the detection comparison circuit 30 detects the detection target W. Is difficult because the change in oscillation amplitude is large.
On the other hand, according to the present embodiment, the stability detection state is detected by the stability detection unit based on the magnitude of the feedback current for maintaining a predetermined oscillation amplitude, and the CPU 50 (stability detection unit) is displayed by the display unit 70 (notification unit). ) Is notified according to the detection.
Therefore, unlike the configuration in which the stable detection state is detected based on the oscillation amplitude as in the detection by the detection comparison circuit 30, the oscillation amplitude varies greatly as in the oscillation circuit 10 using the hard oscillation method. Even when it is difficult to detect stability based on the oscillation amplitude, it is possible to detect the stable detection state of the object W to be detected.

(2) If the oscillation state is stopped according to the distance to the detected object W, there is a possibility that a delay time of rising at the time of oscillation may occur, which is not desirable. On the other hand, according to this configuration, even when the oscillation state is at a distance where the oscillation state is stopped, if the oscillation state is maintained by supplying the feedback current, it is possible to reduce the delay time of rising at the time of oscillation.
Further, the CPU 50 (stability detection means) detects the stability detection state of the detection object W according to the duty of the pulse signal output from the sustain comparison circuit 40. Therefore, the configuration of the feedback circuit used for sustaining the oscillation state can be used for detection of the stable detection state, and the stable detection state can be detected with a simple configuration.

(3) Since the display unit 70 (notification unit) includes a visible display unit 70 (display unit), the display unit 70 (display unit) performs notification according to detection by the CPU 50 (stability detection unit). It becomes possible for the user to visually recognize whether or not the detection object W is stably detected.

(4) According to the present embodiment, the user can change the setting to the optimum reference level for detecting the stable detection state by operating the operation unit 51 according to the detection environment or the like. .

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

( 1 ) Although the detection result indicating whether the CPU 50 is in a stable state is displayed on the display unit 70, the detection result is displayed on a display of an external device such as a PC connected via the output circuit 80. It may be. In such a case, the output circuit 80 corresponds to “notification means” of the present invention.

Block diagram showing electrical configuration of proximity sensor Circuit diagram of oscillation circuit The figure which shows the relationship between the distance to the object to be detected and the oscillation amplitude The figure which shows the relationship between the distance with respect to the to-be-detected object of a proximity sensor, and a duty The figure which shows the relationship between the level of the integral signal in B point of FIG. 3, and the pulse signal output from the comparison circuit for sustaining Flow chart of processing for stability detection Diagram explaining conventional stability detection

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Oscillation circuit 20 ... Integration circuit 25 ... Feedback current supply circuit 30 ... Detection comparison circuit (detection means)
40: Comparison circuit for sustaining 50 ... CPU (stability detection means)
60 ... feedback control circuit 70 ... display section (display means, notification means)
80 ... Output circuit (notification means)
W: Object to be detected

Claims (3)

An oscillation circuit whose oscillation amplitude changes in a hard oscillation mode according to the distance to the object to be detected;
Detecting means for detecting the object to be detected based on a comparison result between an oscillation amplitude of the oscillation circuit and a predetermined detection threshold ;
A feedback circuit for supplying a feedback current for maintaining a predetermined oscillation amplitude in the oscillation circuit ,
The feedback circuit is
A comparison circuit that outputs a pulse signal based on a comparison result between the oscillation threshold and the sustaining threshold lower than the detection threshold;
A feedback current supply circuit that supplies the feedback current according to a pulse signal output from the comparison circuit,
Stability detection means for detecting a stable detection state of the detected object by the detection means, assuming that the amount of the feedback current is equal to or higher than a reference level when the duty of the pulse signal output from the comparison circuit is equal to or greater than a predetermined value ; ,
Proximity sensor comprising: notification means for notifying that the stability detection state has been detected by the stability detection means. Provided with visible display means,
The proximity sensor according to claim 1, wherein the notification unit notifies that the stability detection state is detected by the display unit . The proximity sensor according to claim 1 , further comprising a setting unit capable of setting and changing the reference level for detecting the stability detection state by the stability detection unit .

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