JPH0518644Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to an apparatus for non-contactly measuring the thickness of a sheet-like object such as paper.

B. Prior Art When measuring the thickness of paper, etc. during the manufacturing process, since the object is moving, a non-contact method is desirable. For this reason, electromagnetic measuring devices have been proposed (Japanese Patent Laid-Open No. 54-25755, Japanese Patent Application No. 59-50088, etc.). The principle of these devices is to place the end face of a measurement head that is freely movable perpendicularly to the surface to be measured, facing the surface to be measured, and to measure by sending pressurized fluid to the head and ejecting it from the end face. The head is floated above the surface to be measured, and the pressure of the pressurized fluid is kept constant to keep the flying height constant, and such measurement heads are placed opposite to each other with the sheet to be measured interposed therebetween. Since the distance between the surface of the object to be measured and the end face of the head is kept constant, the distance between the two opposing measurement heads changes depending on the thickness of the sheet to be measured, and the change in this distance The change in the degree of electromagnetic coupling between the two measurement heads is detected and used as a signal indicating the thickness of the sheet to be measured.

C. Problems to be solved by the invention The previously proposed devices described above have the following problems. In the sensor described in JP-A-54-25755 mentioned above, the sensor housed in the measuring head has a coil wound around an iron core. Since the induced electromotive force is extracted and used as the detection output, it is necessary to have two heads facing each other with the object to be measured in between. measurements cannot be taken. In the sensor described in Japanese Patent Application No. 59-500588, one has a built-in head with a coil wound around a magnetic core, and the other head has only a magnetic core, and detects changes in inductance due to changes in the distance between the magnetic cores. Therefore, even if the sheet is in contact with a roll, the thickness can be measured from only one side of the sheet by considering the roll itself as the magnetic core.
The fact that the lead wire is coming out from the head is JP-A-54-
Same as No. 25755.

The measurement head needs to be able to move freely in the direction perpendicular to the surface to be measured, but if a lead wire is drawn out from the head as described above, it is impossible to reduce the rigidity of this lead wire to zero. Because I can't
The vertical movement of the head is inevitably somewhat restricted, resulting in a decrease in measurement accuracy and sensitivity. There is also the problem that when used for a long period of time, the lead wires may break due to metal fatigue. This invention enables thickness measurement on only one side of the sheet to be measured, and prevents the lead wire from protruding from the head itself, ensuring free movement and enabling high-accuracy, high-sensitivity thickness measurement. This is what I am trying to do.

D. Means for solving the problem The sensor housed in the measurement head and the external measurement circuit are coupled by electromagnetic coupling, and in this electromagnetic coupling, the magnetic core around which the coil on the sensor side is wound is shaped like a bar. The coil on the measurement circuit side can move freely in the axial direction on the same magnetic core, and the conductor piece is placed facing the measurement head with the sheet to be measured in between, and the measurement surface of the measurement head is The distance between the measurement head and the surface to be measured was kept constant by ejecting pressurized fluid from the surface facing the surface.

E. Effect Since the coupling between the sensor and the signal extraction circuit is electromagnetic coupling and not coupling by lead wires, the measurement head can move completely with respect to the surface to be measured, resulting in high precision and high sensitivity. It will be done. Also, since the measurement head is placed only on one side of the sheet to be measured, and the other side is just a piece of conductor, the measurement head is placed on one side of the sheet with both sides free, and the piece of conductor is placed on the other side. In the case of a sheet running against a roll, the roll can also be used as a conductor strip on the opposite side of the measuring head. In either case, the thickness is measured by detecting changes in the inductance of the sensor due to changes in the distance between the sensor in the measurement head and the conductor piece on the opposite side.

F. Embodiment FIG. 1 shows an embodiment of the present invention. 1 is a sheet to be measured, 2 is a conductor piece placed under the sheet to be measured, and 3 is a measurement head. The conductor piece 2 and the measurement head are held movably in a direction perpendicular to the surface of the sheet to be measured 1, and an air outlet is provided on the end surface facing the sheet surface, so that each end surface is maintained at a constant distance from the sheet surface. It's becoming like that.

In the measurement head 3, S is a sensor, and the magnetic core C1
A coil K1 is wound around the coil K1. This coil K1 is connected in the measuring head to a coupling coil K2. C2 is the magnetic core of the coupling coil. Outside the measurement head 3, OSC is an oscillator, and K3 is a coupling coil, which is positioned on the same axis as K2 so as to be electromagnetically coupled with coil K2.C2 is common to the magnetic core of coil K3 and loosely passes through coil K3. are doing. The coil K3 is fixed in position, and one end of the coil K3 is connected to one output terminal of the oscillator OSC.
The other end is connected to the inverting terminal of the operational amplifier A, and a feedback coil K4 is connected between the inverting terminal and the output terminal of the operational amplifier. With this configuration, the output voltage of the oscillator acts on both ends of the coil K3. When the distance between the head 3 and the conductor piece 2 changes due to a change in the thickness of the sheet 1, the coil K1
The electromagnetic coupling state between and the conductor piece 2 changes. An eddy current is formed in the conductor piece 2, and the inductance of the coil K1 changes as the coupling state changes. This change in inductance appears as a change in the voltage across the coil K3, and this voltage change, that is, the voltage amplitude of the output of the oscillator OSC changes, and this amplitude change is magnified and appears in the coil K4. This amplitude change is converted into a direct current and detected by the detection amplifier circuit D, and this becomes information on the thickness of the sheet to be measured.

As shown in FIG. 2, the measuring head 3 is a cylindrical body whose side surfaces are supported by air bearings 4 so as to be movable in the vertical direction, and pressurized air is supplied into the measuring head through a separate air supply hole 5. ing. The lower end surface of the cylinder is a bottom body 6 made of plastic, and an air outlet 7 is opened therein. Since the bottom body 6 is made of plastic, it has no electromagnetic influence on the coil K1. By ejecting pressurized air from the air outlet 7, the measurement head 3 is made to float a certain height above the surface to be measured against gravity. The conductor piece 2 has the same structure as the measuring head 3, and the bottom surface of the cylinder (in this case, the top surface of the cylinder) is not made of plastic but a conductor, and is electromagnetically coupled to the coil K1. The lower end of the cylindrical body is supported by a spring and is brought into pressure contact with the underside of the seat, but is kept at a certain distance from the underside of the seat by the jet of pressurized air.

When the bottom surface of the sheet to be measured is supported by rolls at two positions, front and back of the measurement head 3, the position of the bottom surface of the sheet is regulated to a constant value, so the conductor piece 2 can be fixed close to the bottom surface of the sheet. good.

Also, when the sheet is running in contact with a roll, the roll can also be used as a conductor piece.
There is no need to provide a separate conductor piece 2.

FIG. 3 shows an example of the arrangement of the air jet ports 7 on the end face of the measuring head 3, in which four are provided at 90° intervals on the end face.
Every other hole has a large area opening and a small area opening. According to this arrangement, the pressure distribution between the lower end surface of the measurement head and the opposing sheet surface is high in the direction along the X-axis over a wide width as shown in FIG. As shown in Figure 4 Y, the width of the peak of the pressure distribution is narrow. For this reason, if the X-axis direction of the sheet running in contact with the roll is parallel to the roll generatrix, high pressure areas will be distributed over a wide range in the roll generatrix direction.
The measuring head can be kept floating above the sheet without being affected by the diameter of the roll, and can be used even for sheets that are in contact with rolls of small diameter, compared to openings with the same area in each direction on the end face. , it becomes possible to use a measuring head.

Effects The thickness measuring device of the present invention has the above-mentioned configuration, and the measuring head and the measuring circuit are electromagnetically coupled and there is no lead wire, so it is durable and the measuring head can move freely. The measurement accuracy and sensitivity have been improved, and the measurement principle is to detect changes in the degree of electromagnetic coupling due to changes in the distance between the sensor and the opposing conductor piece, so it can be used as a conductor piece to guide the sheet travel. The device can be simplified by using rollers, etc.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the electrical configuration of an embodiment of the present invention, Fig. 2 is a longitudinal cross-sectional side view of the measuring head in the same embodiment, and Fig. 3 shows the shape and arrangement of the air outlet on the end face of the measuring head. FIG. 4, which is a plan view of an example, is a graph showing the pressure distribution on the lower end surface of the head in the same embodiment. 1... Sheet to be measured, 2... Conductor piece, 3... Measurement head, OSC... Oscillator, A... Operational amplifier,
D...Detection amplification circuit, 7...Air jet port.

Claims (1)

[Scope of utility model registration request] An electromagnetic sensor is housed in a measurement head that is held slidably in the axial direction and has a pressurized fluid outlet on the end face facing the sheet surface to be measured so that it is a certain distance away from the sheet surface to be measured. However, when electromagnetically coupling this electromagnetic sensor and an external measurement circuit, the magnetic core around which the coupling coil on the sensor side is wound is made into a rod shape, and the magnetic core on the external measurement circuit side is connected to this magnetic core. The distance between a coupling coil that is loosely inserted in the axial direction and a conductor piece that is fixedly placed opposite the electromagnetic sensor with a sample sandwiched therebetween and where an eddy current is generated by the inductive action from the electromagnetic sensor. A sheet thickness measuring device that detects changes in the thickness of sheets.