JPH0653806A - Displacement detecting sensor - Google Patents

Abstract

PURPOSE:To detect the displacement of an object without being influenced by the dispersion of an oscillation coil or a temperature sensor in displacement detecting sensor and to display an error in the detected displacement. CONSTITUTION:A sensor part 1 is provided with an oscillation circuit 4 having an oscillation coil 3 and a thermistor 5 to be a temperature sensor. A CR oscillation circuit 6 is connected to the thermistor 5 and counters 9, 10 for measuring the frequency of respective oscillation circuits 4, 6 are connected to the circuits 4, 6. A temperature correction table memory 13 for correcting the outputs of the couters 9, 10 corresponding to respective temperatures is previously prepared. Since an error is increased in accordance with the increment of displacement from a reference position used at the time of preparing the table memory 13, the error can be displayed by judging the displacement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting sensor for non-contact detection of displacement due to approach of an object to be detected.

[0002]

2. Description of the Related Art A conventional high-frequency oscillation type proximity switch has an oscillation circuit provided with an oscillation coil and oscillates at a constant frequency. I am trying to detect.
For example, in the proximity switch shown in FIG. 11, the oscillation circuit 101
An oscillating coil 102 is provided to oscillate at a constant frequency, and its output is given to a detection circuit 103. The detection circuit 103 detects the output, converts it into a DC level signal, and linearizes it by a linearizer 104 to obtain a signal corresponding to the distance. Then, in the comparison circuit 105, this signal is discriminated based on the set value set by the user, so that the signal is output when the object comes close to a specific distance.

[0003]

In such a conventional proximity switch, however, the change in temperature is larger than the change in the conductance of the oscillation coil 102 due to the arrival of an object. Therefore, in order to eliminate the effect of temperature, a temperature compensating element 107 such as a thermistor is connected to the feedback circuit section of the oscillation circuit 101 to perform temperature compensation. However, variations in the conductance temperature characteristics of the oscillation coil 102 and variations in the thermistor constants have an effect, which makes it difficult to obtain a proximity switch that is highly accurately compensated for temperature.

The present invention has been made by paying attention to such a conventional problem, and is capable of accurately displacing an object without being affected by variations in the temperature characteristics of the oscillation coil and the thermistor. An object of the present invention is to provide a displacement sensor that can detect and display the accuracy.

[0005]

According to the present invention, there is provided a first oscillation circuit having an oscillation coil, the oscillation frequency of which changes when an object to be detected approaches the oscillation coil, and a temperature change of the first oscillation circuit. A second oscillating circuit whose oscillating frequency changes according to the first and second oscillating circuits, first and second counting means for counting the oscillating frequencies of the first and second oscillating circuits, and respective temperatures of the first oscillating circuit in the operating temperature range To calculate a calculation value to be obtained by the second counting means corresponding to the first counting table, and to generate the first counting table, and to generate the first counting table corresponding to each temperature of the first oscillation circuit in the operating temperature range. The count values obtained by the counting means are respectively generated as second and third count tables, and the data of the second and third count tables are proportionally distributed to correspond to the calculated values at each temperature of the first table. The calculated value to be obtained from the first counting means The reference count N _R of the first counting means is subtracted from the arithmetic value, the fourth correction value ΔN at each temperature
By calculating the counting table of
A correction table memory that uses the fourth counting table as correction table data, a temperature correction processing unit that calculates a correction value ΔN corresponding to the count value M _T of the second counting means by proportional distribution using the correction table, and a temperature correction process. Addition means for adding the correction value ΔN obtained from the section and the reference value N _R, and the addition value (ΔN of the addition means from the count value Ns of the first counting means
+ N _R ), and a display unit for displaying the measurement accuracy corresponding to the level of the absolute value from the reference position N _R based on the distance data Nd obtained by the subtraction unit. To do.

[0006]

According to the inventions of claims 1 and 2 having the above characteristics, the first count table is generated by first calculating the calculation value to be obtained by the second counting means. . Then, the temperature of the first oscillation circuit is continuously changed within the use range, and the count values obtained from the first and second counting means corresponding to each temperature are used as second and third counting tables. Then, by calculating the proportional distribution of the data of the second and third counting tables, the calculated value to be obtained from the first counting means corresponding to the counted value at each temperature of the first counting table is calculated, and the reference count value N The fourth table of the correction value ΔN is obtained by subtracting _R. A correction table is generated by using the fourth counting table of ΔN and the first counting table as correction table data. Then, using this correction table, the correction value ΔN corresponding to the temperature at that time is obtained from the count value M _T obtained from the second counting means. Then, the distance information Nd that does not depend on the temperature is obtained by adding it to the reference value N _R and subtracting it from the count value N _S from the first counting means. Further, the accuracy of the displacement detection sensor corresponding to the displacement from the reference position is discriminated based on the output of this data Nd, and the discrimination result is displayed by the display means.

[0007]

1 is a block diagram showing the overall construction of a displacement detecting sensor according to an embodiment of the present invention. In this figure, this displacement detection sensor is shown as a sensor unit 1 and other electronic circuit unit 2
Composed of. The sensor unit 1 is provided with a first oscillating circuit 4 having an oscillating coil 3 and a temperature detecting element such as a thermistor 5 as shown in the figure. Here, it is assumed that the sensor unit 1 has an oscillating coil 3 on its front surface, and that when the object approaches, the oscillating frequency f _S changes depending on the distance to the object.

The electronic circuit section 2 is provided with a second CR oscillator circuit 6 having the thermistor 5 as one resistance.
The oscillation frequency of the CR oscillation circuit 6 and f _T. The outputs of the oscillator circuit 4 and the CR oscillator circuit 6 are given to the frequency dividing circuits 7 and 8, respectively. The frequency dividing circuits 7 and 8 divide the oscillation frequency by 1 / Ks and 1 / Kt, respectively.
s and Kt can be set. The frequency-divided outputs are given to the counters 9 and 10, respectively. Further, the electronic circuit section 2 has a reference clock oscillator 11 having a constant frequency, for example, a clock frequency of 10 MHz and 4000 Hz, and the respective clock signals are given to the counters 9 and 10. The counters 9 and 10 are counters for counting the number of clocks of the reference clock oscillator 11 by using the frequency-divided output as a gate signal, and constitute the first and second counting means together with the frequency dividing circuits 7 and 8 and the reference clock oscillator 11, respectively. is doing. Here, the count value of the counter 9 is set to N _S , and the counter 1
The count value of 0 is N _T, and these outputs are given to the microcomputer 12. The microcomputer 12 is connected to a temperature correction table memory 13 and a linear correction table memory 14, which are tables for correction described later. These memories 13 and 14 are composed of E ² PROM, for example. The microcomputer 12 performs temperature correction processing using this temperature correction table, converts it into displacement data, and linearizes it using a linear correction table. Then, it is compared with the position data set by the setting unit 15, and is displayed on the display unit 16 and is output from the output unit 17.

Next, detailed functional blocks in the microcomputer 12 will be described with reference to FIG. In the microcomputer 12, a temperature correction processing unit 21 that calculates a correction value ΔN in the number of pulses of the current temperature with respect to the reference temperature based on the temperature correction table memory 13 that corrects the count value M _T from the counter 10. It is provided. A reference value output unit 22 that outputs a reference value N _{R of the} number of pulses is provided. This reference value N _R is set to 25600 in this embodiment. This ΔN and the reference value N _{R of the} pulse number are added by the adding means 23.
Given to. The adding means 23 adds these, and the output thereof is given to the subtracting means 24. The subtracting means 24 calculates the addition value N _R + ΔN from the count value N _S of the counter 9.
For subtracting Nd (= N _S − (N _R + Δ
N)) is calculated. Then, this Nd is given to the displacement calculation processing unit 25 as displacement information. Displacement calculation processing unit 25
Is for linearizing this, and displacement information ± Δd from the reference position is obtained. This displacement information is given to the subtraction unit 26 and the comparison unit 27. As will be described later, a threshold value for determining whether or not Δd is within a predetermined width of the reference position is set in the comparison unit 27, and determines the accuracy of this displacement detection sensor. The discrimination output is displayed on the display unit 1.
Given to 6. Further, the position information of the reference position set by the user is set as IN1 in the setting unit 15. The subtracting means 26 is a subtracting means for subtracting the set value IN1 set by the setting unit 15 from the displacement information of ± Δd. By doing so, the displacement information from the set position is converted, and this value is displayed on the display unit 16. Further, the displacement from the set position is compared with the input value IN2 by the comparison unit 28, and the comparison output is given to the output unit 17.

Next, the processing in the temperature correction processing section 21 will be described in detail. In this embodiment, first, the temperature of the sensor unit 1 is detected by the thermistor 5 in the sensor unit 1.
The CR oscillation circuit 6 oscillates at an oscillation frequency corresponding to the resistance R of the thermistor 5. Therefore, the temperature information of the sensor unit 1 can be obtained from the oscillation frequency. Now, the resistance value R of the thermistor 5 at an arbitrary temperature T is determined by the following equation. R = R ₀ expB (1 / T-1 / T ₀ ) ... (1) T: arbitrary temperature (° K) R: resistance value at temperature T T ₀ : reference temperature (° K) R ₀ : Resistance value B at reference temperature T ₀ : B constant

The creation of the temperature correction table used in the temperature correction process will be described. The oscillation frequency of the CR oscillation circuit 6 is the resistance value R of the thermistor 5, that is, the temperature and the characteristic B.
It depends on the constant. In this embodiment, the individual data of the thermistor 5 and the count value of the counter 9 due to the peculiar variation of the oscillation coil 3 are fetched as data, and the correction is performed based on this. FIG. 3 is a block diagram showing a correction table generation device 30 for creating the temperature correction table 13 based on the data of these individual elements. In this figure, each block having the same reference numeral as in FIG. 1 is the same as that in FIG. 1, and the sensor unit 1 itself having the oscillation coil 3 and the thermistor 5 unique to each displacement sensor is placed in the constant temperature bath 31. The temperature of the constant temperature bath 31 is controlled by the controller 32. Then, the count values N _S and N _T of the counters 9 and 10 corresponding to the oscillation frequencies f _S and f _T at the predetermined temperature are obtained. Then, the outputs from the counters 9 and 10 are written in the data memory 34 via the data writing unit 33. The data memory 34 is composed of an E ² PROM.

[0012] Referring now to accurately temperature, for example -10 ° C. and + 60 ℃ definable in a thermostat 31, M _T table calculating section 35 calculates the resistance value of the thermistor 5 from the oscillation frequency at this temperature, whereby B Calculate the constant. In this way, the resistance value of the thermistor 5 at an arbitrary temperature can be calculated.

Next, for all the temperatures at which this displacement sensor can be used, in this embodiment, from -30 ° C to 78 ° C, the resistance value with respect to the temperature of the thermistor in steps of 2 ° C is determined. Then, the oscillation frequency of the CR oscillation circuit 6 and the count value M _T of the counter 10 corresponding to this oscillation frequency are calculated from each resistance value. And M at each temperature
_{The T} value is written in the M _T table area in the data memory 36. FIG. 4A shows the M _T thus calculated.
It is a 1st counting table which shows the change of a value. Where M _T
The table calculation unit 35 is a first counting table calculation unit that calculates a calculation value at each temperature obtained from the second counting unit.

Now, as shown in FIG. 3, the sensor unit 1 is actually put in the constant temperature bath 31 and the control unit 32 is operated to change the temperature. FIG. 6 is a graph showing changes in the count value N _S of the counter 9 with respect to the distance d to the object. As shown in this figure, the detection area of the distance d to the object is 100%, and the distance (50%) to 1/2 of the detection area is the reference distance d _R. The reference temperature at this reference distance d _R, which is the N _S value of 24 ° C. in this embodiment, is used as the reference value N _R. Set N _R to be 25,600 pulses. For example, reference clock oscillator 1
When the first clock frequency of 1 is set to 10 MHz, the frequency division number Ks is changed to set the output pulse width of the frequency division circuit 7 to 2.56 ms. The reference value N _R thus obtained can be output from the reference value output unit 22 shown in FIG. Further, the M _T value at this reference temperature is set to be 8000 pulses, for example. In this case, the frequency dividing number K of the frequency dividing circuit 8
By changing _T to make the output pulse width 2 seconds and counting the second clock frequency of 4000 Hz of the reference clock oscillator 11, the number of pulses of 8000 is obtained.

Then, by continuously changing the temperature of the thermostatic bath 31 with the sensor unit 1 placed in the thermostatic bath 31, the MT value and the M _T value in steps of 2 ° C. at each temperature from −30 ° C. to 78 ° C. Get the N _S value. And this data is shown in Figure 5.
Data is written in the data memory 34 as shown in (a) and (b). Note the temperature at this time is not strictly defined, is used to know the relationship N _S values for M _T values. Here, the data writing unit 33 uses the count values N _S and M _T obtained by the first and second counting means at each temperature in the operating range of the oscillator circuit 3.
To constitute a second counting table generating means. The tables of FIGS. 5A and 5B thus obtained are the second and third tables.

[0016] Now N _S table calculating unit 37 from the table of M _T obtained in thus obtained was calculated as shown in the table and figure M _T and N _S in FIG. 5 4 (a), N _S value at each temperature Is calculated and written in the data memory 36. That is, FIG. 4 (a)
Corresponding to each M _T value of the M _T table of FIG. 5, the M _T values before and after that are searched for from the table of FIG. Then, the N _S value corresponding to each M _T value in FIG.
It is calculated as shown in (b). Also, the ΔN table calculation unit 3
8 is the N _S value at each temperature thus obtained and the reference temperature,
Here, ΔN is calculated from the difference from the N _S value (= N _R = 25600) at 24 ° C., which is shown in FIG. 4 (c).
The data is written in the data memory 36 as a table (fourth table). Here, the N _S table calculation unit 37 is shown in FIG.
A third count for calculating the calculated value to be obtained by the first counting means corresponding to the calculated value at each temperature in the table of FIG. 4A by proportionally distributing the data of the counting table shown in FIG. 4B. The N _S table calculating unit 38, which is a table calculating means, calculates a fourth table of the correction value ΔN by subtracting the reference count value N _R from this table Δ
It constitutes N table calculation means.

Thus, as shown in FIGS. 4 (a) and 4 (c), a pair of tables in which the ΔN values corresponding to M _T at each temperature are written are stored in E of the temperature correction table memory 13 shown in FIGS. ² Data is transferred to PROM and used as a temperature correction table. Note here forms a table for the N _S value once corresponding to each temperature, as shown in FIG. 4 (b), by subtracting a predetermined reference value N _R from this value, shown in FIG. 4 (c) Δ
Although the N table is generated, it goes without saying that the ΔN table may be directly generated after the proportional distribution.

In FIG. 6, the curve A is the distance d at the reference temperature.
Is a graph showing the change of the N _S value with respect to, and the curve obtained by using data from a large number of specific displacement sensors is used as it is. Then, at a temperature higher than the reference temperature, the number of pulses N _{S with} respect to the distance d
Changes as shown by the curve B, and changes as shown by the curve C at low temperatures. Therefore, the difference Nd from the reference value is calculated by subtracting ΔN from N _S , and converted to the curve A to obtain the distance data based on the corrected pulse number Nd.

Here, the curves B and C shift up and down according to the temperature, but ΔN is calculated assuming that they are both parallel to the curve A. However, as shown in FIG. 6, ΔN can be accurately calculated at the reference distance d _R , but if the distance is far from the reference distance d _R, these curves are not parallel and the error gradually increases. Therefore, a predetermined width before and after the reference distance d _R ,
For example, as shown by hatching in FIG. 7, less correction error before and after the reference distance d _R, the range of error becomes larger as the distance from the reference distance d _R. Comparison unit 27
Depending on the value of Δd, for example, the range of 40% to 60% is the high precision region (FINE region), the range of 0 to 40% and 60 to 100% is the medium precision region (ROUGH region), and 100% or more is Even if the operation is performed, it is determined as a low-precision area (NG area).

FIG. 8 is a graph showing changes in the number Nd of temperature-corrected pulses with respect to the distance d. This graph uses a prescribed curve obtained based on the data of a plurality of displacement sensors, and by fitting this to the distance information d. Then, 256 of Nd is changed by 1%, and data corresponding to this distance is held in the linear correction table 14 as shown in FIG. In this correction table, for example, in a portion where the curve has a small inclination, distance data d ₁₀ , d _11, ... Are sequentially recorded in the table T1 in 0.5% units. Further, in the portion where the distance is shorter than the reference distance d _R , the distance is sequentially recorded by the table T2, the tables T3, T4, ... The distance Δd from the actual reference distance d _R is obtained by the following equation (2).

[Equation 1] Here, P is the number of data from the reference position. The first term of the equation (2) is the sum of displacements when n is 0 to P-1,
The term indicates the proportional distribution value of the distance with respect to the pulse number Nd within the displacement.

The value of ± Δd thus obtained and the setting unit 15
The comparison unit 28 compares the value IN2 set in step 1. Then, the detection signal up to the object is output according to the relationship with the position set by the user.

Next, the operation of this embodiment will be described. First, the sensor unit 1 of the displacement detection sensor is arranged in the measurement area up to the object. When an object approaches the oscillating coil 3, the oscillating circuit 4 oscillates at the oscillating frequency f _S corresponding to the distance d to the object. Further, the CR oscillation circuit 6 oscillates at the oscillation frequency f _T corresponding to the temperature at this time.
Therefore, the count value M _T of the counter 10 corresponding to the temperature is obtained. Figure 4 The M _T (a), corrected by the temperature correction table memory 13 shown in (c), ΔN at the temperature of the sensor unit 1 by obtaining a proportional distribution values of .DELTA.N
Is obtained. In this way, ΔN and N _R are added by the adding means 23, and the subtracting means 24 obtains the difference from N _S to obtain a distance d that does not depend on the temperature or the element of each displacement sensor.
The pulse number Nd corresponding to Then, by converting this value based on the conversion table as shown in FIGS. 8 and 9, the linearized position information Δd can be obtained. Since this Δd indicates the displacement from the reference value d _R specific to the displacement sensor, it is converted into the displacement from the position IN1 set by the user by the setting unit 15. Then, this value is displayed on the display unit 16 and the displacement from the user's reference position is compared by the comparison unit 28 to obtain an output for the distance to the predetermined displacement.

Then, depending on the range of Δd, "FINE", "ROUGH", "N" are inputted by the comparison unit 27 as described above.
The area of “G” is discriminated, and the same is displayed on the display unit 16.

FIG. 10A shows a pair of outputs OUT1 and OUT2 as shown in the figure depending on whether the displacement from the reference position IN1 set by the user exceeds IN2. In this case, the comparison unit 28 identifies whether or not the absolute value of the displacement from IN1 exceeds IN2. Further, as shown in FIG. 10B, the reference position I
N1 and the position IN2 farther from this may be set, and a pair of outputs OUT1 and OUT2 may be output accordingly.

In this embodiment, the thermistor is used as the temperature sensor connected to the second oscillation circuit, but it goes without saying that various temperature sensors can be used instead of the thermistor.

Further, in this embodiment, the accuracy of the measurement error is displayed stepwise by the comparison unit, but it goes without saying that the level of the display error can be displayed in more detail by the absolute value of Δd. . Further, in the present embodiment, the accuracy is determined based on the output of the displacement calculation processing unit 25, but it is also possible to determine the accuracy based on the value of Nd before linearization.

[0027]

As described above in detail, according to the present invention, a compensation table memory including temperature compensation means unique to each displacement sensor and a variation with respect to the temperature of the oscillating coil is prepared for temperature compensation, and this data is stored in the compensation table memory. Is corrected based on. Therefore, there is no temperature compensation error due to variations in the oscillation coil and the temperature sensor, and the displacement of the object can be accurately measured. Since the range of this error is determined and displayed, there is an effect that it is possible to accurately recognize how much error is displayed at that position.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a displacement detection sensor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing functional blocks of a microcomputer of this embodiment.

FIG. 3 is a block diagram showing a configuration of a correction table generation device for creating a correction table memory 13 according to the present embodiment.

4A is an M _T table obtained by calculation according to the present embodiment, FIG. 4B is a pulse number Nd corresponding thereto, and FIG.
Is a table showing the correction value ΔN.

5 (a) is a table showing the M _T values at each temperature obtained when inserting the sensor unit in a thermostat at temperature range of the displacement detection sensor, (b) is in that case N _T It is a table showing a value.

FIG. 6 is a graph showing changes in the number of pulses N _S with respect to the distance in this example.

FIG. 7 is a diagram showing a display of a measurement error and an error range with respect to a distance to an object.

FIG. 8 is a temperature-compensated Nd with respect to the distance d in the present embodiment.
It is a graph which shows change of a value.

FIG. 9 is a diagram showing a conversion table for linearizing Nd in the present embodiment.

FIG. 10 is a diagram showing a correspondence of output with respect to distance in the present embodiment.

FIG. 11 is a block diagram showing a configuration of a conventional high frequency oscillation type proximity switch.

[Explanation of symbols]

1 Sensor Section 2 Electronic Circuit Section 3 Oscillation Coil 4 Oscillation Circuit 5 Thermistor 6 CR Oscillation Circuit 7, 8 Frequency Division Circuit 9, 10 Counter 11 Reference Clock Oscillator 12 Microcomputer 13 Temperature Correction Table Memory 14 Linear Correction Table Memory 15 Setting Section 16 Display unit 17 Output unit 21 Temperature correction processing unit 22 Addition unit 23 Reference value output unit 24, 26 Subtraction unit 25 Displacement calculation processing unit 27, 28 Comparison unit 30 Correction table generating device 31 Constant temperature bath 32 Control unit 33 Data writing unit 34 , 36 data memory 35 M _T table calculation unit 37 N _S table calculation unit 38 ΔN table calculation unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akimitsu Ogata 10 Odoroncho, Hanazono Doudocho, Ukyo-ku, Kyoto City, Kyoto Prefecture

Claims (2)

[Claims] 1. A first oscillating circuit which has an oscillating coil and whose oscillating frequency changes when an object to be detected approaches the oscillating coil; and an oscillating frequency which changes due to a temperature change of the first oscillating circuit. A second oscillating circuit, first and second counting means for counting oscillating frequencies of the first and second oscillating circuits, and the first oscillating circuit corresponding to each temperature of the first oscillating circuit in a working temperature range. The first counting table is generated by calculating the calculation value to be obtained by the second counting means, and the first and second counting means are associated with each temperature of the first oscillation circuit in the operating temperature range. The obtained count values are respectively generated as second and third count tables, and the data of the second and third count tables are proportionally distributed to correspond to the calculated values at each temperature of the first table. Should be obtained from the first counting means The calculated value is calculated, the reference count value N _R of the first counting means is subtracted from each calculated value, and the fourth count table of the correction value ΔN at each temperature is calculated to obtain the first count value. A correction table memory that uses the first and fourth counting tables as correction table data; and a temperature correction processing unit that calculates a correction value ΔN corresponding to the count value M _T of the second counting means by proportional distribution using the correction table. , The correction value ΔN and the reference value N obtained from the temperature correction processing unit
_R and _R , subtraction means for subtracting the addition value (ΔN + N _R ) of the addition means from the count value Ns of the first counting means, and a reference based on the distance data Nd obtained by the subtraction means. A displacement detection sensor, comprising: a display unit that displays the measurement accuracy corresponding to the level of the absolute value from the position N _R. 2. A displacement calculation processing unit that linearizes an output Nd obtained by the subtraction unit with respect to a distance d from the oscillation coil to an object, and the display unit is obtained by the displacement calculation processing unit. A displacement comprising: a comparison unit that determines the accuracy of displacement detection depending on whether displacement data is within a predetermined width before or after a reference position of displacement or outside the range; and a display unit that displays an output of the comparison unit. Detection sensor.