JP3387180B2 - Proximity switch - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch, and more particularly to a proximity switch characterized by its sensitivity adjustment and sensitivity setting.

[0002]

2. Description of the Related Art Proximity switches of high-frequency oscillation type include an amplitude detection type that detects a decrease in oscillation amplitude when an object approaches, and a frequency detection type that detects proximity of an object based on a change in frequency. In general, an amplitude detection type proximity switch is widely used as a proximity switch for detecting magnetic metal.
FIG. 13 is a block diagram showing an example of a conventional amplitude detection type proximity switch. In this figure, an oscillating circuit 2 is configured together with a parallel resonance circuit 1 of an oscillating coil L and a capacitor C. The output of the oscillation circuit 2 is detected by the detection circuit 3,
The signal processing circuit 4 detects a decrease in the oscillation level. When the decrease in oscillation is detected, the object detection signal is output via the output circuit 5. The power supply circuit 6 supplies power to each block. Here, the oscillation circuit 2 is connected with a sensitivity adjustment resistor Re for adjusting the sensitivity.

FIG. 14 is a circuit diagram showing an example of an oscillating circuit 2 configured together with the parallel resonant circuit 1. In the figure, the parallel resonance circuit 1 includes a resistor R1 and diodes D1 and D2.
The base of the transistor Q1 is connected via. A constant current is supplied to the base of the transistor Q1 from the power source, and resistors R2, R3, and R4 are connected in series between the base of the transistor Q1 and the ground terminal. The middle point of the resistors R2 and R3 is connected to the base of the transistor Q2, and the emitter thereof is connected to the sensitivity adjusting resistor Re described above. Transistors Q3 and Q4 are provided on the collector side of the transistor Q2.
Is connected to the current mirror circuit, and a current having the same current value as that of the power supply flowing in the transistor Q2 is fed back to the parallel resonant circuit 1 via the transistor Q4 to form a positive feedback loop and oscillate. FIG. 15A is a graph showing the relationship between the oscillation amplitude and the distance to the detection object when the sensitivity adjustment resistance Re changes from small to large. As is clear from this figure, oscillation suddenly starts and stops at a specific position at a distance to the object. Such oscillation is called hard oscillation.

FIG. 16 is a block diagram showing an example of a frequency detection type proximity switch. In this figure, the sensor head 11
It shows a separation type proximity switch in which the signal processing unit 12 and the signal processing unit 12 are separated. The sensor head 11 includes a parallel resonance circuit 11a including a coil and a capacitor and a temperature detection element 11b. Further, the signal processing unit 12 has an oscillating circuit 13 connected to the parallel resonant circuit 11a, and its output end is connected to a frequency counter 14.
The frequency counter 14 detects the oscillating frequency of the oscillating circuit, and its output is connected to the signal processing unit 15a composed of the microcomputer 15. Further, the temperature sensitive element 11b of the sensor head 11 is input to the temperature detection circuit 16 in the signal processing unit 12. The temperature detection circuit 16 outputs temperature information to the microcomputer 15. The microcomputer 15 determines the presence / absence of an object using a predetermined frequency as a threshold value, and its output is output from the output buffer circuit 17 via the output port 15b. When the sensitivity is set, the signal is input from the setting unit 18 to the signal processing unit 15a via the input port 15c.

In such a frequency detection type proximity switch, the frequency f continuously changes with respect to the distance L to the object as shown in FIG. 15 (b). Therefore, it is known that the operating distance is adjusted by teaching the threshold level.

[0006]

However, the above-mentioned amplitude detection type proximity switch has the following drawbacks. Since the sensitivity adjustment is performed manually by changing the sensitivity adjustment resistance Re, there is a drawback in that the adjustment requires skill and the operator may have variations in the adjustment position. Since the rotation angle of the variable resistor of the sensitivity adjustment resistor Re is not proportional to the detection operation distance, it is difficult to adjust it to the optimum point, and it is necessary to repeat the adjustment and the operation confirmation depending on the feeling. Especially when a long-distance operating point is set, the change in the conductance of the oscillation coil becomes small depending on the presence or absence of the detection object. Therefore, there is a drawback that it is difficult to adjust to the optimum point, and the operating point changes greatly even if the position of the variable resistor is slightly displaced due to vibration or the like. Further, the proximity switch is most often used only for detecting the passage of an object, but in this case also, it is necessary to adjust the variable resistance and confirm the operation with the object arranged. Especially, when the object is difficult to move, there is a drawback that the adjustment becomes difficult.

On the other hand, the frequency detection type proximity switch has the following drawbacks. The change in oscillation frequency due to the approach of an object is smaller than the change in conductance in an amplitude detection type proximity switch,
Frequency fluctuations due to operating temperature greatly affect the operating point. Therefore, a temperature detection circuit is required, and temperature compensation processing in the microcomputer is required, but it is necessary to perform screening and correction for each unit, which has a drawback that the manufacturing process becomes long and complicated. In the proximity switch having a structure in which the sensor head is separated from the proximity switch main body, the sensor head is associated with the main body, so that flexibility in use is lost. Therefore, even if only one of them was damaged, it was necessary to replace the whole. Furthermore, the sensor head requires a temperature detection element,
Miniaturization becomes difficult. Further, since the number of connecting cables between the sensor head and the main body side increases, there is also a drawback that the connecting process also increases. Further, since the threshold is determined from the presence or absence of the detected object when setting the sensitivity, even when the sensitivity setting does not particularly require high accuracy, such as the simple detection of the passage of the detected object, the detected object is close to the object and there is no object. There is a drawback in that the teaching is required twice depending on the state and the operation becomes complicated.

The present invention has been made in view of the problems of the conventional method for adjusting the sensitivity of the proximity switch.
The purpose is to easily set the sensitivity without making the structure complicated and to be able to determine an abnormality at the time of setting the sensitivity.

[0009]

The invention according to claim 1 of the present application
Is the distance Lon for detecting the approach of the oscillation coil and the object.
The distance Loff for detecting the separation of
A hysteresis circuit that changes the oscillation state according to the body detection signal
For switching between the oscillation circuit including and the feedback current of the oscillation circuit
Therefore, the sensitivity adjustment circuit that adjusts the sensitivity and the sensitivity adjustment circuit
Output of the switch signal to the circuit
Switch control means for adjusting the
Oscillates based on the output of the detection circuit and the detection circuit
Signal processing means for determining the presence or absence of an object by the stop
And a teaching switch to input the teaching status
, And the hysteresis circuit has distances Lon and L
Change the hysteresis width, which is the difference from off, in multiple steps
The switch control means should detect the object.
When the teaching switch is turned on when it is not
Adjust the feedback current to the maximum adjustable range from the oscillation start state
Feedback current when oscillation is stopped by continuously changing until oscillation stops
Detection of I (N1) and oscillation of feedback current
The feedback current I (N2) at the start of oscillation
Detecting the object and moving the object close to the position to be detected
When the teaching switch is turned on in
The maximum flow adjustable range is from the oscillation start state to the oscillation stop state.
The feedback current I (N
Second feedback current updating means for detecting 3)
And the feedback current I detected by the second feedback current updating means.
If (N3) is smaller than I (N2), hysteresis of hysteresis circuit
The process of the second feedback current updating means is made smaller by narrowing the theresis width.
Repeat the process and newly detect by the second feedback current updating means.
When the generated feedback current I (N3) is smaller than I (N2)
A third abnormality detecting means for detecting the inability to set
Feedback current when no abnormality is detected by the normal state detection means
I (B) is I detected by the second feedback current updating means.
Second sensitivity setting set between (N2) and I (N3)
Means and having.

The invention of claim 2 of the present application is the proximity of claim 1.
In the switch, feedback by the second feedback current updating means
Determines the state where oscillation does not start when the current is at the maximum value
Characterized by having a first abnormality detecting means for
Is.

The invention of claim 3 of the present application is the same as that of claim 1 or 2.
In the proximity switch of, the second feedback current updating means
Oscillation stops until the feedback current changes to the minimum state
Second abnormality detecting means for determining an abnormality when not
It is characterized by having.

[0012]

[0013]

In the invention of claim 6 of the present application, the oscillation circuit is
The present invention is characterized by having a plurality of differential circuits that change the distance for detecting proximity and the distance for detecting separation in a plurality of steps.

[0015]

In the invention of claim 1 of the present application, the work presence / absence test is performed.
Do not bring the object to be detected in the approach, or
Teachings are placed in a state where they should not be detected.
Switch on the switch. At this time, the second feedback current updating means
The feedback current gradually increases, and the feedback current I when the oscillation is stopped
(N1) is detected. The feedback current is gradually reduced from the oscillation stopped state.
Feedback current I (N2) at the point where oscillation is made smaller by gradually decreasing
To detect. Amplitude characteristic curve changes depending on the hysteresis circuit
Therefore, I (N1) and I (N2) have different values. Next
Titin while keeping the object close to where it should be detected
Switch on. At this time, set the resistance value of the feedback current to the maximum.
The feedback current I (N
3) is detected. Then, I (N2) and I (N3) are compared.
By comparison, the state that does not turn off by the hysteresis circuit is determined
If this is the case, reduce the hysteresis width of the hysteresis circuit
The process of is repeated. Thus again I (N2) and I (N
Compared with 3), it is not turned off by the hysteresis circuit.
If the condition is determined, this is set as an abnormal condition in advance.
Do not set. On the other hand, if there is no abnormality, I (N2) and I
The feedback current is set to the intermediate value of (N3)
It

Further, in the inventions of claims 2 and 3, the above-mentioned operation is performed.
In addition to the above, the difference does not start when the feedback current is maximum.
Ordinarily, when the feedback current is at a minimum and the oscillation does not stop,
I always try to judge.

[0017]

1 is a block diagram showing the structure of a high-frequency oscillation type proximity switch 20 according to a first embodiment of the present invention.
In the figure, the same parts as those of the conventional amplitude detection type proximity switch described above are denoted by the same reference numerals and detailed description thereof will be omitted.
Also in this embodiment, the oscillator circuit 2 is configured together with the LC parallel resonance circuit 1. Then, the oscillation circuit 2 is provided with a sensitivity adjustment circuit 21 for adjusting its sensitivity. The sensitivity adjustment circuit 21 is an adjustment circuit for adjusting the oscillation sensitivity by changing the sensitivity adjustment resistance of the oscillation circuit based on a switch signal from the outside. In the present embodiment, the mode changeover switch 22 for changing the mode of the proximity switch between the operation mode "RUN" and the set mode "SET" for sensitivity setting,
Also, a teaching switch 23 used for teaching is provided. The signals from these switches are input to the microcomputer 24. The microcomputer 24 performs teaching without a work based on inputs from the mode changeover switch 22 and the teaching switch 23, and sets a sensitivity set value in the sensitivity adjusting circuit 21 by a switch signal as described later. Constitutes a means. The output of the oscillation circuit 2 is sent to the microcomputer 2 via the detection circuit 3.
4 to the signal processing means 24a. Signal processing means 2
Reference numeral 4a is for discriminating the presence or absence of an object by discriminating the output level of the detection circuit 3 by a predetermined threshold value as in the conventional example, and the output thereof is outputted to the outside through the output circuit 5. Further, the signal processing means 24a switches the oscillation state of the oscillation circuit 2 at the time of detecting an object and provides a hysteresis so as to detect a small fluctuation in the position of the object or a malfunction due to noise or the like.

FIG. 2 is a circuit diagram showing the configuration of the parallel resonant circuit 1, the oscillator circuit 2 and the sensitivity adjusting circuit 21 of this embodiment.
In this figure, the same parts as those of the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted. Also in this embodiment, the parallel resonant circuit 1 includes the diodes D1 and D2 and the transistor Q1.
The oscillator circuit 2 having Q4 is connected. _A resistor group composed of resistors _RA , _RB1 , _RB2 , _RB3 ... Is connected in parallel to the position of the sensitivity adjusting resistor Re of the oscillator circuit 2, as shown in the figure. Each of the resistors R _B1 , R _B2 , R _B3, ...
1, SW2 ... Are connected in series. These switches are opened and closed based on a switch signal from the microcomputer 24, and a parallel combined resistance is used instead of the resistance Re described above. Therefore, the sensitivity of the oscillation circuit can be adjusted under the control of the microcomputer 24. Here, switch this switch to SW
There are eleven switches from 1 to SW11, and the resistors connected in series to them are also R _{B1 to} R _B11 . These resistances R _{B (i)}
Shall resistance becomes ^{_{R Bi = R 0 · 2 i}} (i = 1~11) are set. By doing this, the switches SW1 to S
By turning on and off the 11-bit switch of W11, the combined resistance value Re can be set in 2048 steps. A transistor Q5 is connected to the oscillator circuit 2 in parallel with the resistor R4. The transistor Q5 is turned off in the oscillating state, and turned on when the oscillation stops due to the approach of an object to reduce the feedback current. By doing so, it is possible to make a difference between the distance Lon at which the object comes close to the proximity switch and is on and the distance Loff at which it is off. Hereinafter, this difference in distance is referred to as a hysteresis. The transistor Q5 is controlled by the output of the signal processing means 24a of the microcomputer 24 described above. Here, transistor Q5 and resistor R
Reference numeral 4 constitutes a differential circuit in the oscillation circuit 2.

FIG. 3A is a graph showing changes in the conductance g of the coil of the parallel resonant circuit 1 with respect to the set distance L to the detected object (work), and FIG. 3B is the value of the sensitivity adjustment resistance (composite resistance) Re. FIG. 6 is a graph showing a change in the operating distance L until the oscillation is stopped, and FIG. 7C is a diagram showing a relationship between the proximity switch and the detection object in the no teaching. FIG. 4 is a flowchart showing the entire operation when sensitivity adjustment (teaching without a work) is performed without using a detection object. At the time of teaching without a work, first, in step 31, the mode changeover switch 22 is set to "RU".
From "N" to "SET" mode. At this time, FIG. 3 (c)
It is assumed that the detection object is not approached in front of the proximity switch 20 as shown in FIG. Then, the teaching switch 23 is first depressed. By doing this, the routine proceeds to the routine 33, and the workless teaching process is executed.

FIG. 5 is a flow chart showing the operation of the teaching process without a work. Sensitivity adjustment circuit 21
Is the resistance value of the sensitivity adjusting resistor corresponding to the pointer n. The pointer n has, for example, 11 bits, that is, a value of 0 to 2047. In Re (0), all the switches SW1 to SW11 are turned on to set Re to the minimum state, and in Re (2047), all the switches SW1 to SW11 are set. SW
11 is off, that is, Re is in the maximum state, and during this period, it changes corresponding to n. First, in step 51, the pointer n is set to 0 and the sensitivity adjustment resistor Re is set to Re.
(0), that is, set to the minimum value. Then, the routine proceeds to step 52, where it is checked whether the amplitude of oscillation is less than or equal to the threshold value Vth of the signal processing means 24a. At this time, since Re is the minimum value, when a normal sensor head is connected, the oscillation circuit 2 oscillates at a steady value when the object is not approaching, and the oscillation amplitude exceeds the threshold value. . However, in the case of disconnection or incorrect connection, the threshold value may not be exceeded. Therefore, in this case, the process proceeds to step 53 and error processing 1 is performed.

When a normal sensor head is connected and the oscillation circuit oscillates at a steady value, the amplitude level is sufficiently higher than the threshold value Vth of the signal processing means 24a. At this time, the routine proceeds to step 54, where the pointer n is incremented and Re (n) is set in the sensitivity adjustment circuit 21 via the output port. Then, the routine proceeds to step 55, where it is checked whether or not n has reached the maximum value, in this case 2047. If it is below the maximum value, the routine proceeds to step 56, where it is checked whether or not the amplitude of oscillation is reduced and is below the threshold value. If it is not less than the threshold value, the process returns to step 54, the pointer n is further incremented, and the same processing is repeated. In this way, the amplitude of oscillation becomes less than or equal to the threshold value before n reaches the maximum value, 2047 in this case. However, in some abnormal state, for example, when a sensor head that cannot be connected is connected, the oscillation amplitude level may be high even if n is maximized. In this case, the process proceeds to step 57 and the error process 2 is executed. To do.

In a normal case, the amplitude sharply decreases at a specific value of the sensitivity adjusting resistor, and the oscillation stops. Then, the process proceeds from step 56 to step 58 to turn on the transistor Q5. Further, in step 59, the sensitivity adjustment resistance value Re (n) at this time is set to Re (N1).
In this way, the oscillation circuit 2 suddenly stops oscillating at a constant value of Re. This indicates the point where the curve indicating the oscillation stop becomes horizontal in FIG. Therefore, the distance L1 at this time is the maximum detection distance of the sensor head of the parallel resonance circuit 1. Therefore, in order to detect the object stably, it is necessary to set a distance shorter than this.

Then, in step 60, the pointer n is decremented. Then, in step 61, it is checked whether or not the amplitude exceeds the threshold value Vth, and the processes of steps 61 and 62 are repeated until it exceeds. If the threshold value is exceeded, the process proceeds to step 62, where the value of Re (n) at that time is Re
(N2). This Re (N2) is used for teaching with or without a work described later. And step 64
Proceed to step No and the sensitivity adjustment resistance Re (A) in teaching
Is determined by the relationship with Re (N1). That is Re
(A) is a predetermined coefficient α for the resistance value of Re (N1), for example,
It may be a value multiplied by 0.7 to 0.8 (where 0 <α <
1). The value obtained by subtracting the constant value Rx from Re (N1) is R
It may be set as e (A). Here the microcomputer 24 when the teaching switch 23 is turned on in step 51,54,56,58,59, continuously increase the sensitivity adjustment resistor from the smallest oscillation starting state of the adjustment range until the oscillation stops, Re The function of the first resistance value updating means 24b for detecting (N1) is achieved, and in steps 52 and 53, when the sensitivity adjusting resistance Re is set to the minimum value, the abnormal state is judged when the amplitude is below the threshold value. The function of the first abnormality detecting means 24c is achieved. The microcomputer 24 also executes steps 55 and 57.
In the above, when the oscillation stop is detected in step 64, the function of the second abnormality detecting means 24d for detecting the abnormality when the oscillation does not stop even when the resistance value Re of the sensitivity adjusting resistor becomes maximum is achieved. Resistance value R of the sensitivity adjustment resistor
The function of the first sensitivity setting means 24e for calculating the sensitivity adjustment resistance Re (A) to be set from e (N1) is achieved.

When the routine 33 is finished, the sensitivity setting is completed only by teaching without a work. Therefore, the mode selector switch 22 is switched to "RUN" to proceed to the normal operation mode. In this case, R set here
The distance Lona with respect to e (A) is the set distance in the no teaching. In this state, the transistor Q5 is off, and the object can be detected if the detection object 26 passes within this distance Lona in FIG. 3 (c). Since the transistor Q5 is turned on after the object is detected, the distance Loffa at which it is turned off next is Lona as shown in FIG.
It will be a longer distance.

Next, the proximity switch 2 according to the second embodiment of the present invention.
0A will be described with reference to FIG. In this figure, the same parts as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted. Also in this embodiment, the parallel resonance circuit 1 and the oscillation circuit 2 are configured, and the output thereof is input to the microcomputer 25 via the detection circuit 3. The output circuit 5, the sensitivity adjustment circuit 21, the mode changeover switch 22 and the teaching switch 23 are the same as those in the first embodiment.
In the present embodiment, teaching with and without a detected object is performed twice, and teaching with or without a work is performed by which the optimum threshold value is set. This teaching can be used for the purpose of detecting only the protruding portion of the detection object having a step.

FIG. 7A is a graph showing changes in the conductance of the coil with respect to the set distance L to the work,
(B) is a graph showing changes in the value of the sensitivity adjustment resistance (composite resistance) Re and the operating distance L until the oscillation is stopped
(C), (d) is a figure which shows the relationship between the proximity switch 20 and the detection object 27 at this time. FIG. 8 is a graph showing a change in oscillation amplitude with respect to the sensitivity adjustment resistance Re. The teaching with or without a work is used for detecting a protrusion 27a protruding toward the proximity switch side in a detection object 27 having a step as shown in FIG. 7C, for example. In this case, the non-protruding portion of the detection object 27 is first made to face the proximity switch 20A, the "SET" mode is set, and the teaching switch 23 is pressed for the first time. The distance between the proximity switch 20 and the detection surface of the detection object 27 at this time is L2. Then, the routine proceeds to the routine 43 through steps 41 and 42 shown in FIG. Routine 43 is a routine 3 for teaching without a work shown in FIG.
The same process as 3 is performed. In this case, the sensitivity adjustment resistance Re (n) is gradually increased as shown in FIG. Then, n is sequentially incremented in the loop of steps 52 to 55. When Re reaches a predetermined value, the oscillation amplitude gradually decreases along the curve A in FIG. Then, in step 56, the resistance value of A1 exceeding the threshold value is set to Re (N1) in step 59. In step 58, the transistor Q5 is turned on, so that the Re-amplitude curve goes from the curve A to the point B1 on the curve B.
Then, by decreasing Re (n) in the loop of steps 60 and 61, the curve B rises to the upper right. When the amplitude reaches the point B2 where the amplitude exceeds the threshold value in step 61, the transistor Q5 is turned off, and the curve A is returned to again. The value at this time is Re (N2). For teaching with / without work, step 45
Then, without setting the mode changeover switch 22 to "RUN", the protrusion 27a of the detection object 27 is made to face the proximity switch 20A and the teaching switch 23 is pushed down as shown in FIG. 7D. Proximity switch 20 at this time
The distance between A and the detection surface of the detection object 27 is L3. When the switch 23 is pressed, the routine proceeds from step 45 to the routine 46, and the teaching with / without work is executed.

As shown in FIG. 10, the routine 46 first sets the sensitivity adjustment resistance to Re (0), that is, the minimum value in step 71, as in the routine 33. Then, the transistor Q5 is turned off, the process proceeds to step 73, the pointer n is incremented, and a new sensitivity adjustment resistor Re (n) is added.
To set. Then, the process proceeds to step 74, and it is checked whether the amplitude at that time is less than or equal to the threshold value. If it is not less than the threshold value, the process returns to step 73 and the same processing is repeated. At this time, it moves to the lower left along the Re-amplitude characteristic curve C in FIG. In this way, when the point C1 on the curve C is reached and becomes equal to or less than the threshold value, the process proceeds to step 75, and the sensitivity adjustment resistance Re (n) at that time is set to Re (N3). This distance L
Let g ₃ be the conductance of the coil at ₃ . Then, in step 76, Re (N2) and Re (N3) are compared. If Re (N3) is smaller, curve C is curve A
Since it is not between the curve B and the curve B, it is not in the undetectable state.
However, if Re (N2) is smaller, curve C becomes curve A.
Since it is between B and B and cannot be detected as will be described later, the routine proceeds to step 76 and error processing is performed. Re
If (N2) is larger, it is not in the undetectable state.
Proceeding to step 77, the sensitivity adjustment resistance value Re (B) during teaching with and without work is set to Re (N2) and Re (N
Set to the intermediate value of 3). These median values are preferable for Re (B), and Re (B) = {Re (N2) + Re (N
3)} / 2.

FIG. 11 shows the change in the oscillation amplitude with respect to the distance L to the object when the sensitivity adjustment resistance Re (B) set in this way is set as the sensitivity value of the oscillation circuit 2. Here, Re (B) is the same as Re (N2) and Re described above.
Although it is an intermediate value of (N3), Re is 11 as described above.
It is expressed in bits, and is completely Re (N2) and Re
In some cases, it cannot be half of (N3). The object is Lon
Transistor Q when approaching within b and detecting an object
Since 5 is turned on, the threshold distance becomes long. If this distance Loffb is larger than the distance L2 at the time of teaching in FIG. 7C, even if the base portion 27b of the detection object 27 faces the proximity switch 20A, the object is not in the non-detection state. Therefore, this is an abnormal state in which the object detection state is always obtained. This is a case of detecting the detection object 28 or the like in which the interval between the protrusion 28a and the base 28b is small in FIG. 11, and shows that the curve C is between the curves A and B in the curve of FIG. There is. This abnormality occurs when the sensitivity adjustment resistance value Re (N2) is smaller than Re (N3). Therefore, this abnormality is detected in step 76, and the process proceeds to step 78 to perform error processing. In this way, the threshold value is not set in the state where an error occurs, so that malfunction can be prevented in advance.

The rise where the microcomputer 25 when the teaching switch 23 is turned on in step 51,54,56,58,59, the sensitivity adjustment resistor from the smallest oscillation starting state of the adjustment range continuously until the oscillation stops The second resistance value update for detecting Re (N1), detecting the resistance value Re (N2) of the sensitivity adjustment resistor at the start of oscillation by sequentially decreasing the resistance value of the sensitivity adjustment resistor from that value after the oscillation is stopped. Has achieved the function of means 25b,
Steps 52 and 53 achieve the function of the first abnormality detecting means 25c that determines an abnormal state when the amplitude is equal to or smaller than the threshold value when the sensitivity adjustment resistance Re is set to the minimum value. Also, the microcomputer 25 detects the abnormality when the oscillation does not stop even if the resistance value Re of the sensitivity adjusting resistor becomes maximum in steps 55 and 57.
The function of 5d is achieved. Also microcomputer 2
In step 5, when the teaching switch is turned on for the second time in steps 71 to 75, the sensitivity adjustment resistance is continuously increased from the oscillation start state of the smallest adjustable range to the oscillation stop, and the resistance value Re (N3) is detected. The function of the third resistance value updating means 25e is achieved, and the function of the third abnormality detecting means 25f for detecting the setting failure is achieved when the resistance value Re (N3) is larger than Re (N2) in step 76. Therefore, based on the resistance values Re (N2) and Re (N3) of the sensitivity adjustment resistor when the oscillation stop is detected by the second resistance value updating means in step 77, the sensitivity adjustment resistor Re ( The function of the second sensitivity setting means 25g for setting B) is achieved.

When this routine 46 is completed, the routine proceeds to step 47, where the mode changeover switch 22 is set to "RUN".
Check if the condition is reached. In the "RUN" state, the presence / absence of an object is determined based on the sensitivity adjustment value Re (B) set by teaching with or without a work.
In this way, as shown in FIG. 11, the distances Lonb and Loffb are set as threshold distances, and the protrusion 2 of the detection object 27 having a step is formed.
It can be adjusted to detect only 7a.

In this embodiment, the state in which the oscillation is stopped is not detected in step 71, but an abnormality detection function for detecting an abnormal state in which the oscillation is stopped is provided as in steps 52 and 53 in FIG. It may be provided. Further, as in steps 55 and 57 in FIG. 5, in steps 73 and 74, an abnormality detection function may be provided to detect an abnormal state in which oscillation does not stop even when n reaches the maximum value.

In the present embodiment, the transistor Q5 is turned on and off to provide a hysteresis for the set distance, but as shown in FIG. 8, when the curve C is between the curves A and B, detection cannot be performed. Becomes In this case, it is also possible to reduce the width of the hysteresis to enable detection. FIG. 12 is a circuit diagram showing a configuration of an oscillation circuit and a sensitivity adjustment circuit having such two types of hysteresis. The same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment, instead of the resistor R4 and the transistor Q5, resistors R4a and R4b are connected in series,
A switching transistor Q6 is connected between the resistor R4a and the ground terminal, and a switching transistor Q7 is connected between the resistor R4b and the ground terminal. Then, in the normal mode, the transistor Q7 is kept in the off state at all times, and the transistor Q6 is turned on / off in place of the transistor Q5 in steps 58, 62, and 72 of the above-mentioned flowchart. In step 76, Re (N2) is Re
If it is larger than (N3), the transistors Q6 and Q7 are switched and the transistor Q6 is always turned off.
The transistors Q7 may be turned on / off at 62 and 72. In this case, the differential distance Loff −
Since Lon becomes small, the distance between the curves A and B in the curve of FIG. 8 becomes small, and a detection object having a minute step can be detected. Since the transistor Q7 also enters an error state in step 76, error processing is performed.

In this embodiment, the feedback current is switched and the sensitivity is adjusted by changing the resistance value of the sensitivity adjusting resistor, but the sensitivity can be adjusted by directly switching the feedback current from the control means. . In this case, the sensitivity adjustment resistor is in inverse proportion to the feedback current, so
Increasing the resistance value of the sensitivity adjusting resistor in the embodiment corresponds to decreasing the feedback current. Further, the first feedback current updating means detects the feedback current I (N1) instead of Re (N1), and the second feedback current updating means Re (N1), Re.
It is assumed that the feedback currents I (N1) and I (N2) are detected instead of (N2), and the feedback current I (N3) is detected instead of Re (N3). Further, the third abnormality detecting means is the feedback current I.
If (N3) is smaller than I (N2), hysteresis of hysteresis circuit
The process of the second feedback current updating means is made smaller by narrowing the theresis width.
Repeat the process and newly detect by the second feedback current updating means.
When the generated feedback current I (N3) is smaller than I (N2)
It is intended to detect the non-set. The first sensitivity setting means sets the feedback current I (A) based on the feedback current I (N1), and the second sensitivity setting means sets the feedback current I (N).
I (B) based on (N1), I (N2), I (N3)
Shall be set. Further, although the high frequency oscillation type proximity switch has been described in the present embodiment, the teaching and the abnormality detection according to the present invention can be applied to the hard oscillation type proximity switch in which oscillation rapidly starts at a certain distance.
That is, even in the capacitance type proximity switch, if the operating distance can be continuously changed from the outside, the teaching and the abnormality detection according to the present invention can be applied.

[0034]

According to the first aspect of the invention, the detection having a step is provided.
Since there is a threshold value for the object in the middle of the step, there is no work
I am teaching. Also at this time, the oscillation circuit
The third abnormality is that the off state cannot be detected due to the hysteresis.
If it is detected by the detection means, reduce the hysteresis distance.
By repeating the same process, an object with a small step
Is also able to be detected. Further oscillation times
If the off state cannot be detected due to the hysteresis of the road,
Abnormal condition is detected. Therefore, an object with a small step
Operates without accidentally setting the sensitivity setting value for
Can be ensured.

According to the inventions of claims 2 and 3,
By providing the first and second abnormality detecting means,
It is possible to detect an abnormal connection or disconnection of the head.

[Brief description of drawings]

FIG. 1 is a block diagram of an amplitude detection type proximity switch according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an oscillation circuit and a sensitivity adjustment circuit according to a first embodiment of the present invention.

3A is a graph showing a conductance of a coil with respect to a work setting distance, and FIG. 3B is a graph showing a change in a value of a sensitivity adjustment resistance Re for starting / stopping oscillation with respect to an operating distance;
(C) is a diagram showing a relationship between a proximity switch and a detected object in the non-teaching.

FIG. 4 is a flowchart showing an entire teaching process of this embodiment.

FIG. 5 is a flowchart showing an operation of teaching without a work.

FIG. 6 is a block diagram of an amplitude detection type proximity switch according to a second embodiment of the present invention.

7A is a graph showing a conductance of a coil with respect to a work set distance, and FIG. 7B is a graph showing a change in a value of a sensitivity adjustment resistance Re for starting / stopping oscillation with respect to an operating distance;
(C), (d) is a figure which shows the relationship between a proximity switch and work in teaching with or without work.

FIG. 8 is a graph showing a change in oscillation amplitude with respect to the sensitivity adjustment resistance Re.

FIG. 9 is a flowchart showing the entire operation of teaching with or without a work.

FIG. 10 is a flowchart showing a teaching process with or without a work.

FIG. 11 is a diagram showing a work that can be detected and a work that cannot be detected by teaching with or without a work according to the present embodiment.

FIG. 12 is a circuit diagram showing an example of an oscillator circuit having a plurality of hysteresis circuits that change the distance of hysteresis.

FIG. 13 is a block diagram showing the overall configuration of a conventional amplitude detection proximity switch.

FIG. 14 is a circuit diagram showing an oscillation circuit of a conventional amplitude detection proximity switch.

15A is a graph showing the amplitude of the oscillation circuit with respect to the work setting distance L of the amplitude detection type proximity switch, and FIG.
6 is a graph showing a change in oscillation frequency with respect to a work set distance.

FIG. 16 is a block diagram showing an example of a conventional frequency detection type proximity switch.

[Explanation of symbols]

1 parallel resonant circuit 2 oscillator circuits 3 Detection circuit 4 Signal processing circuit 5 output circuits 20, 20A proximity switch 21 Sensitivity adjustment circuit 22 Mode selector switch 23 Teaching switch 24,25 microcomputer 24a, 25a Signal processing means 24b First resistance value updating means 24c, 25c First abnormality detecting means 24d, 25d Second abnormality detecting means 24e First sensitivity setting means 25b Second resistance value updating means 25e Third resistance value updating means 25f Third abnormality detecting means 25g Second sensitivity setting means 27,28 Detection object

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masazumi Ueda, Omron Co., Ltd., No. 10, Hanazono Dodo-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture (56) Reference JP-A-5-218845 (JP, A) JP-A-63- 302376 (JP, A) JP 59-207740 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03K 17/00

Claims (3)

(57) [Claims] 1. An oscillating circuit including an oscillating coil, and a differential circuit for changing an oscillating state according to a detection signal of an object such that a distance Loff for detecting an object separation is longer than a distance Lon for detecting an object approach. A sensitivity adjustment circuit that adjusts the sensitivity by switching the feedback current of the oscillation circuit, a switch control unit that adjusts the sensitivity of the oscillation circuit by outputting a switch signal to the sensitivity adjustment circuit, and an output of the oscillation circuit. A detection circuit for detecting, a signal processing means for determining the presence or absence of an object by oscillation or its stop based on the output of the detection circuit, a teaching switch for inputting a teaching state,
And the hysteresis circuit has a plurality of hysteresis widths that are differences between the distances Lon and Loff.
It is intended to vary the floor, the switch control means, continuously from highest oscillation starting state of the adjustment range the feedback current when the teaching switch in a state that should not detect the object is turned until the oscillation stops To detect the feedback current I (N1) when the oscillation is stopped, and to sequentially increase the feedback current from the value in the oscillation stopped state to detect the feedback current I (N2) when the oscillation is started. When the teaching switch is turned on in the state of being brought close to the position to be detected, the feedback current is continuously changed from the oscillation start state to the oscillation stop state with the largest adjustable range, and the feedback current I ( Second feedback current updating means for detecting N3) and the feedback current I detected by the second feedback current updating means.
If (N3) is smaller than I (N2),
By reducing the hysteresis width, the second feedback current update procedure
Repeat the process at the stage to newly update the second feedback current
The feedback current I (N3) detected by the means is I (N2)
Third anomaly detection means for detecting inability to set when the size is too small
And the feedback current I (B) is set to an intermediate value between I (N2) and I (N3) detected by the second feedback current updating means when no abnormality is detected by the third abnormal state detecting means. A proximity switch having a second sensitivity setting means. 2. The proximity according to claim 1, further comprising: first abnormality detecting means for determining a state where oscillation does not start when the feedback current is maximized by the second feedback current updating means. switch. 3. A second abnormality detecting means for determining an abnormality when oscillation is not stopped before the feedback current is changed to the minimum state in the second feedback current updating means. The proximity switch according to Item 1 or 2 .