JPS60168001A - Electrostatic capacity type position detecting device - Google Patents

Abstract

PURPOSE:To improve an accuracy of a position detecting device by connecting a sensor part and an electronic converting circuit part by a special coaxial tube cable, and also widening an effective area of a probe of a sensor. CONSTITUTION:As for a sensor 11' of an electrostatic capacity type, its detecting area is wide remarkably. A special coaxial tube cable 6, a converting circuit 12, an indication adjusting part 9 and a display lamp are provided. When the sensor 11' having a wide probe area is used, a variation of an electrostatic capacity following a passage of an object to be detected 3 becomes large, therefore, an S/N can be improved, and also a detecting distance between the object 3 to be detected and the sensor 11 can be enlarged as shown by D. The distance D can be enlarged up to 250mm.. Since an area of a sensor prove is large, a variation of an electrostatic capacity following a passage of the object to be detected becomes large, therefore, a control point is set easily to an optional detecting position.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a capacitive position detection device that detects the position of a moving metal object by changing capacitance.

(Problems with conventional technology) Conventionally, steel plates, pipes,
When detecting the position of wire rods etc. without contact, as shown in Figure 1, there are capacitance type, high frequency oscillation type, microwave type,
The position of the object to be detected is detected using a detection device called a proximity switch, such as a magnetic type or a photodetection type.

FIG. 1 is a schematic diagram showing the main parts of such a conventional example. In the figure, (1) is a proximity switch, (2) is a conveying means such as a roller, (3) is an object to be detected such as a steel plate that moves in the direction of the arrow, and (4) is a power supply and signal conductor. However, the conventional proximity switch has a sensor part (1) as shown in Figure 2.
1) and the electronic conversion circuit i (1 (Ig)) are integrated, so if the sensor part (1 凰) is a capacitance type, the area of the sensor probe (detection electrode) is small. ,
Due to sensitivity, the distance (detection distance) d between the proximity switch (1) and the detected object (3) cannot be increased, and even at room temperature, the detection distance d is very small, about 30 mm.

Therefore, there is not only a risk that the proximity switch (1) may come into contact with the detected object (3) and be damaged, but also
When the temperature reached a high temperature, the conversion circuit (1□) was affected by the heat and became unusable.

Therefore, an apparatus was devised that can be used at temperatures ranging from 1000 to 200 degrees centigrade. FIG. 3 is a schematic diagram showing the main parts of such a conventional example. In the figure, the first and second
Partial pressures corresponding to those in the figure are given the same reference numerals. (5)
is a heat-resistant coaxial cable, which separates the sensor section (11) and the conversion circuit section (12) for heat resistance. FIG. 4 is a partially cutaway view showing an example of such a heat-resistant coaxial cable. In this type of position detection device, a high-frequency electrical signal is applied between the sensor (11) and the detected object (3), so a coaxial cable is used to prevent the weak high-frequency signal from attenuating and to make it less susceptible to external noise. need to be used.

In Fig. 4, (51) is the inner conductor, (52) is the polyethylene or Teflon insulator, (53) is the outer conductor, (
54) is coated with vinyl chloride or Teflon.

The inner conductor (51) is made of a thin single wire or stranded wire made of soft iron, and the outer conductor (53) is made of a braided copper wire.

In FIG. 3, when the temperature is below 200'C, the heat-resistant coaxial cable (5) as described above can be used due to the heat resistance of the Teflon coating. However, when the temperature exceeds 500° C., the sensor part (1x) made of heat-resistant cast steel or steel plate can withstand it sufficiently, but in the conventional cable (5) as described above, the physical properties change as well as the material. For example, the dielectric constant changes, and the distributed capacitance of the cable (5) changes. A device for detecting capacitance changes cannot be used if the capacitance of the cable (5) changes significantly. Furthermore, since it is strongly influenced by heat, it is difficult to increase the area of the sensor probe.

In the case of FIG. 3 as well, since the detection button @d cannot be made large, there is a drawback similar to that of FIG. 1. In both the cases of Figs. 1 and 3, there is a change in detection sensitivity over time. In addition, in these devices, the lamp was turned on when the object to be detected (3) passed over the sensor part (11), but the object to be detected (3) was a steel plate covered with rust (scale). In such cases, malfunctions could occur.

Furthermore, since the area of the sensor part (11) is small, it will not operate unless the detected object (3) completely covers the sensor part (11), and if the moving speed of the detected object (3) increases, the lamp will not work. There was also a problem with the lighting being delayed.

(Object of the Invention) An object of the present invention is to provide a capacitance type position detection device which has significantly improved the following drawbacks.

(Summary of the invention) The present invention uses a capacitance type sensor, and separates the sensor section and electronic conversion circuit section using a special coaxial cable in which an internal conductor is arranged in a hollow coaxial tube. In addition, the above object has been achieved by increasing the effective area of the sensor probe.

(Example) FIG. 5 is a partial sectional view showing an example of a special coaxial tube cable used in the present invention. In the figure, (6) shows the special coaxial tube cable as a whole, (61) shows the internal conductor, (
62) is a coaxial tube (which also serves as an external conductor), (63) is a spacer, (64) is a lock nut, and (6b) is a socket. (7) is a pipe for protecting the cable (6) from thermal radiation of high temperature objects as necessary. The internal conductor (61) is passed through the hole of the spacer (63), and the internal conductor (61) is supported by the hole K at the center of the coaxial tube (62). The coaxial tube (62) is made of high temperature carbon steel tube or the like.

The internal conductor (6D) uses twisted wire.

The special coaxial tube cable (6) having such a configuration had a capacitance value of 20 pF per 1 m when a coaxial tube (6 g) having a diameter of, for example, % inch was used. Since the minimum capacitance value of a conventional heat-resistant coaxial cable is 60 pF per 1 m, the unit length capacitance value of the above-mentioned special coaxial tube cable (6) is reduced to 1/3. This means that
This means that the cable transmission distance will be tripled. In addition, since the insulator of the special coaxial tube cable (6) is air, changes in relative permittivity due to temperature changes can be ignored, and 50
Even at high temperatures of 0° to 1000° C., a heat-resistant coaxial cable with small capacitance and small change in capacitance can be obtained. Therefore, there is an advantage that the heat-resistant material can be freely selected.

FIG. 6 is a schematic diagram showing a preferred embodiment of the present invention using such a special coaxial tube cable. In the figure, parts corresponding to those in FIG. 3 are given the same or similar symbols. (11) is a capacitance type sensor, but the difference from the above-mentioned sensor (11) is that the effective area of the sensor's globe (detection electrode) is significantly larger. The sensor (11) is supported by a support including an insulator as in the case of (1st construction), but it is not shown in the figure. If a sensor (11) with a large probe area is used, the change in capacitance due to the passage of the object (3) will increase, so the S/N ratio can be improved and the distance between the object (3) and the sensor (11) can be improved. ) can be increased as shown by the detection distance between According to experiments, the distance is 2
I was able to increase the size to 50u.

In Figure 6, (6) is a special coaxial tube cable, (8)
is a general cable, (9) is an indicator adjustment section, (1G is an indicator lamp, and as shown in Figures 3 and 6, the sensor part (ll
).

(11') and the conversion circuit (12) using a heat-resistant coaxial cable (
When connecting using 5) and (6), the capacitance value of the heat-resistant coaxial cable becomes a problem. In the case of Figure 3, the heat-resistant coaxial cable (
5) has a large capacitance value of 1 mfi, and the sensor part (1
Since the maximum capacitance change detected by 1) is about 101) F, the capacitance change actually used for position detection is several pF or less considering the moving speed of the detected object (3). The initial capacitance value of the high-temperature sensor section including the heat-resistant coaxial cable (5) is generally as large as 200 to 400 pF, so if this is included, the capacitance resolution cannot be reduced, and the Setting the control (eg switch) point and basolateral unsteadiness. The minimum capacitance resolution is at most 1.5 to ZpF based on the rotation angle of the control point setting knob.
Therefore, it is impossible to set control points with a resolution lower than that. Therefore, it is possible to set the control point with sufficient resolution even when the capacitance change is less than a few pF.The capacitance value of only the sensor section (11) is obtained by removing the capacitance value of the heat-resistant coaxial cable (5) from the capacitance change value. and use it. In this way, the control points can be set regardless of the initial capacitance value, which is proportional to the length of the heat-resistant coaxial cable (5). In the case of FIG. 6, this technique is used in conjunction with increasing the area of the sensor probe.

The indication adjustment section (9) includes a zero point adjustment section that sets the initial capacitance value to zero when there is no object (3) to be detected, and a sensor section (
11') The capacitance change range is scaled from 00 to 100% of the total length.
A full span adjustment section for setting the detected position, a scale section for indicating the detected position, a control point setting knob for setting an arbitrary position on the sensor (Is') as a control point of the detected object (3), etc. are provided. Thereby, when there is no object to be detected (3), the scale is O1, and when the object to be detected (3) completely covers the force sensor (11'), it is 100, and the control position is determined by the control point setting knob. The moving state of the object to be detected (3) and the operating state of the conversion circuit section (12) can be determined from the indications on the scale, and the control position can be easily set or changed by simply turning the knob. Note that α0) is a lamp that is turned on when a relay or the like is operated when the detected object (3) reaches the control position, but this may be provided integrally with the instruction adjustment section (9).

(Effects of the Invention) The present invention connects the sensor section and the electronic conversion circuit section with a special coaxial tube cable, and at the same time connects the sensor section with the special coaxial tube cable and widens the effective area of the sensor's globe. It is thought that this invention includes two inventions.

The effects of the first invention are as follows.

(al) Since the special coaxial tube cable has a very small capacitance value per unit length, the same detection sensitivity as before can be maintained even if the length of the cable is increased. Therefore, the electronic conversion circuit part can be kept away from heat. Therefore, it is advantageous for high temperatures of 500°C or higher.

(b) Since the insulator of the % special coaxial tube cable is air, the change in dielectric constant due to temperature change can be ignored, and the
Even at a high temperature of 1000°C, the change in capacitance is extremely small. Therefore, it is suitable for a capacitive position detection device,
There is also the advantage of being able to freely select heat-resistant cable materials.

(C) By using a special coaxial tube cable, the effect of heat can be reduced even if the sensor section is enlarged, so it is possible to increase the effective area of the sensor probe.

In addition to the above-mentioned effects, the second invention has the following effects.

(d) Since the effective area of the sensor probe is large, the change in capacitance due to the passage of the object to be detected becomes large, resulting in 8/N
The ratio is improved and the detection sensitivity is improved.

Therefore, since the detection distance can be increased, there is no need to worry about contact between the sensor section and the object to be detected, and the sensor is less susceptible to vibrations and shocks.

(e) Improved detection sensitivity prevents malfunctions even if the object to be detected, for example, a steel plate, has a scale of several 1011 II thick. In addition, the use of a special coaxial tube cable reduces the change in detection sensitivity over time.

(f) Since the area of the sensor probe is large, the change in capacitance due to the passage of the object to be detected becomes large, so it is easy to set a control point at an arbitrary detection position. Therefore, for example, by setting a control point near the passage start position of the detected object, it is possible to prevent a delay in lighting the lamp when the moving speed of the detected object is fast.

(g) Due to the boxed reason, it is possible to know the passing state (travel amount) of the object to be detected and the operating status of the electronic conversion circuit section by looking at the instructions of the indicating adjustment.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the main parts of a conventional example of a position detection device;
The figure shows the configuration of a proximity switch used in this, Figure 3 is a schematic diagram showing an improved example of Figure 1, Figure 4 is a partially cutaway diagram showing an example of a conventional heat-resistant coaxial cable used in this, and Figure 5 The figure is a partial cross-sectional view showing an example of a special coaxial tube cable used in the present invention, and FIG. 6 is a schematic diagram showing a preferred embodiment of the present invention. (11')...Sensor part with large globe area,
(12)...Electronic conversion circuit section, (2)...
Transport means, (3)... Object to be detected, (6)...
・Special coaxial tube cable, (61)...Inner conductor,
(62)...Hollow coaxial tube.

Claims (1)

[Claims] 1. Detecting the position of an object by detecting a change in capacitance between the object being moved by a conveyance means and a capacitance sensor installed opposite the object. A capacitance type position detection device characterized in that the sensor part and the electronic conversion circuit part are connected by a special coaxial tube cable having an internal conductor arranged in the center of a hollow coaxial tube. Detection device. 2. ``When detecting a change in capacitance between an object to be detected that is moved by a conveyance means and a capacitance type sensor installed opposite to it, the capacitance that detects the position of the object to be detected is detected. In the type position detection device, the sensor section and the electronic conversion circuit section are connected by a special coaxial tube cable in which an internal conductor is placed in the center of a hollow coaxial tube, and the surface area of the probe of the sensor is widened. Capacitive position detection device.