JPS6259762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a detector commonly referred to as a differential transformer.

The present inventor invented and filed an application for a differential detector which is especially advantageous for measuring small displacements of detected members (Japanese Patent Application No. 74207/1982). The invention consists of a core that moves according to the movement of the detected member, a primary coil arranged along the movement path of the core and excited by alternating current, and a voltage difference that is proportional to the movement of the core. In a differential detector consisting of a generated secondary coil, the core is formed of a conductive metal with low magnetic permeability (specific magnetic permeability of about 10 ^-3 to 10 ^-6 ), and high frequency excitation (about 50KC to 2MC) is used. A differential detector characterized by applying a current to a primary coil, and in conventional differential transformers, the core is made of a ferromagnetic metal with high magnetic permeability (specific magnetic receptivity of about 10 ³ to 10 ⁶ ), such as iron. It is unique in that it uses conductive metals with low magnetic permeability, such as aluminum, silver, and copper, instead of the ones previously used.

In other words, in conventional differential detectors, the core attracts many magnetic lines of force due to its high magnetic permeability, and as the core moves, these lines of magnetic force also move, causing the voltage induced in the two secondary coils to change, causing the core's mechanical The displacement of the magnetic field is extracted as the output voltage of the differential detector, but since the magnetic field line distribution generated by the primary coil changes as the core moves, and the symmetry of the magnetic field lines breaks down, the displacement of the core and the output voltage are It is difficult to maintain the proportional relationship (linearity) correctly, and various measures are required to maintain the linearity correctly.

On the other hand, in the case of the prior invention, since a conductive metal with low magnetic permeability is used as the core, the magnetic lines of force in the part where the core is present are weakened by the eddy current loss generated in the core, and the voltage induced in the part is reduced. Therefore, if the core moves, the induced voltage in the secondary coil on one side decreases by an amount proportional to the displacement, and the voltage on the other side increases by that amount, and the difference is extracted as the output voltage, but the core has a low Because it is permeable, it does not attract magnetic lines of force, and even if the core moves, the distribution of magnetic lines of force in the coil does not change and always maintains symmetry, so linearity is maintained correctly, especially for short strokes with small width coils. This feature is extremely effective in detectors.

However, even in the case of this prior invention, a drawback was found that if the diameter of the coil was small and the diameter of the core was less than about 5 mm, a large output voltage could not be obtained.

When we think about the reason for this, we find that the distance traveled by the magnetic lines of force generated by the strands of the primary coil due to the excitation current is short due to the high frequency, and when the diameter of the coil is large, almost all of the generated lines of magnetic force reach the core. Since the core passes through the moving bobbin hollow hole, the value of eddy current loss caused by the magnetic field lines is large and the output voltage is large, but as the diameter of the coil becomes smaller and the diameter of the bobbin hollow hole becomes smaller. , the lines of magnetic force generated by the primary coil are distributed outside the bobbin hollow hole, and the number of magnetic force lines existing inside the bobbin hollow hole is reduced, so that the eddy current loss caused by the magnetic force lines when the core passes through the bobbin hollow hole is reduced. It is considered that the value becomes small and therefore the output voltage of the differential detector does not become large.

The present invention was devised for the purpose of eliminating the drawback of a drop in output voltage in such a small-diameter detector as described above, and at the same time obtaining better linearity regardless of the size of the core diameter.

Generally, the eddy current generated in the core flows along the outer surface of the core, so the core of conductive metal with low magnetic permeability does not need to be a so-called rod with the metal all the way to the center, but a ring with a thickness of 1 to 2 mm or less. It is sufficient to use the same shape. In other words, if a ring-shaped core with a thickness of 1 to 2 mm or less is displaced in the axial direction of the differential detector, the same size as when a round bar core is used in the differential detector due to eddy current loss. It produces an output voltage.

Through the ring hole of this thin ring-shaped core, a highly permeable ferromagnetic material with as large an outer diameter as possible, such as an iron rod or tube, is used as an auxiliary core.
Place it so that it spans the entire width of the next coil. The arrangement relationship between the core and the sub-core may be such that the core slides along the sub-core, or the sub-core is passed through the ring hole of the core and fixed to the core, and the width core is used as a support rod for the core.
A structure may be adopted in which the core and sub-core are displaced together. However, in the latter case, the sub-core must be longer than the full width of the primary coil so that it is always arranged over the full width of the primary coil within the displacement range.

As described above, one sub-core of high magnetic permeability ferromagnetic material is inserted into the ring hole of the ring-shaped core of low magnetic permeability conductive metal.
If the secondary coil is arranged to span the full width of the primary coil, almost all of the magnetic lines of force generated by the primary coil are attracted by the ferromagnetic sub-core and pass through the sub-core, reducing magnetic resistance. Not only are the lines of magnetic force generated by the primary coil significantly stronger than in the case of the primary coil, but also the lines of magnetic force are attracted to the sub-core, so the distribution of lines of magnetic force within the hollow hole of the bobbin generated by the elements of the primary coil is improved compared to the case without the sub-core. becomes uniform.

The ferromagnetic sub-core strengthens the magnetic lines of force, thereby increasing the voltage induced in the two secondary coils, but since the sub-core is symmetrically placed across the entire width of the primary coil, the two The voltages induced in the secondary coils are the same, so the output voltage of the differential detector does not change due to this sub-core.

In other words, when the ferromagnetic sub-core is placed across the entire width of the primary coil, the lines of magnetic force in the primary coil are strengthened without causing any change in the output voltage of the differential detector, and the lines of magnetic force are aligned with the bobbin hollow hole. As a result, the eddy current loss occurring in the conductive metal core with low magnetic permeability becomes large, and the output voltage of the differential detector increases. The proportional relationship, that is, the linearity, is improved, and the value of residual zero voltage is also reduced.

The effect of this ferromagnetic sub-core occurs in the same way regardless of the coil diameter.If the coil diameter is small and there is no sub-core, the lines of magnetic force distributed outside the bobbin hollow hole will also be ferromagnetic. Since almost all magnetic lines of force are attracted to the sub-core of the body and pass through it, they exist within the bobbin hollow hole, so there is no possibility that the output voltage of the differential detector will decrease due to the small diameter of the core. do not have.

The eddy current loss We generated in a unit volume is We=1/6ρπ ²・f ²・Bm ²・t ² [W/m ³ ] where ρ: specific resistance π: pi f: frequency Bm: maximum magnetic flux Density is expressed by the formula t: thickness, and is proportional to the square of the frequency, inversely proportional to the resistivity, and proportional to the square of the maximum magnetic flux density. Therefore, the eddy current loss increases as the maximum magnetic flux density increases, so in the case of the present invention in which a ferromagnetic material is arranged as a sub-core to reduce magnetic resistance and increase the magnetic flux density,
Compared to the case without a sub-core, the value of eddy current loss is large, and the value of the output voltage of the differential detector is also large. Furthermore, since the eddy current loss increases as the resistivity of the metal decreases, silver and copper are more advantageous than aluminum in terms of conductive metals with low magnetic permeability in order to increase the output.

In addition, to increase the eddy current loss, it is possible to apply a high-frequency excitation current to the primary coil, but there is a frequency range that can be used by oneself when manufacturing the coil. The frequency to be used is about 50KC to 2MC.

Embodiments of the present invention will be described below with reference to the drawings. The embodiment whose side cross section is shown in FIG. FIG. 5 shows another embodiment in which the core slides along the sub-core. Since the former type is easier to manufacture, this type will probably be used more often in practice.

A primary coil 6, secondary coils 8 and 9 are wound around a bobbin 1 shown in FIG.
2 is configured to be movable, and its connection state is shown in FIG.

A non-magnetic plastic hobbin 1 is provided with two grooves 3 and 4 of the same size around which a coil is wound, and an axial slit 5 through which a lead wire of the coil is guided. 1 at the bottom through the grooves 3 and 4 of the bobbin.
The secondary coil 6 is wound in several layers, and in close contact with the primary coil, the secondary coil 8 is wound on the groove 3 side, and the secondary coil 9 is wound on the groove 4 side the required number of times.

The core 12 that moves within the hollow hole 2 of the bobbin is made of a conductive metal with low magnetic permeability and is formed in a ring shape, and the rod-shaped sub-core 13 made of a ferromagnetic material is attached to the core 12.
The core 12 and the sub-core 13 pass through the ring hole of the bobbin 2 and are fixed thereto, and also serve as a support rod.
It is configured so that it can move in the axial direction. As mentioned above, the length of the sub-core must be longer than the total width of the primary coil. 7 is a lead wire of the primary coil, and 10 and 11 are lead wires of the secondary coil. Then, a high frequency alternating current voltage is applied to both ends of the lead wire 7 of the primary coil.

In the above configuration, a voltage is induced in the two secondary coils 8 and 9 tightly wound around the primary coil by magnetic lines of force generated by the primary coil 6.
When the core 12 is located between the two secondary coils 8 and 9, voltages of equal magnitude are generated in both coils, so the voltage between the lead wires 10 and 11 is zero. When the core 12 moves to the left in FIG. 1, the voltage induced in the secondary coil 8 becomes smaller.
The voltage induced in the secondary coil 9 increases,
The voltage difference is generated between the lead wires 10 and 11. Conversely, if the core 12 moves to the right, the secondary coil 8
The voltage induced in the secondary coil 9 becomes larger, the voltage induced in the secondary coil 9 becomes smaller, and the difference in voltage is generated between the lead wires.

When the displacement of the core 12 is plotted on the horizontal axis and the voltage is plotted on the vertical axis, the generated voltage becomes V-shaped as shown in FIG. This is the same as in the case of a conventional differential transformer.

In the embodiment shown in FIG. 5, the bobbin hollow hole 14 is closed at one end, and the end of a sub-core 17 made of ferromagnetic material is fixed thereto, and the sub-core extends into the hollow hole 14. A core 15 made of a conductive metal with low magnetic permeability is connected to a plastic support pipe 16.
It is attached to the end of the core 17 and is slidable along the sub-core 17.

The other parts are the same as the example shown in FIG. 1, as indicated by the same reference numerals, and the operation is also the same as described for the example shown in FIG. 1, except that the core 15 slides along the sub-core 17.

As described above, the present invention has a core made of a conductive metal with low magnetic permeability formed into a ring shape, and a sub-core made of a ferromagnetic material with high magnetic permeability that extends through the ring hole and extends over the entire width of the primary coil. Because it is made by arranging
Even if the core is displaced, the symmetry of the coil's magnetic field line distribution does not collapse, and the ferromagnetic sub-core makes the magnetic field line distribution uniform in the bobbin hollow hole.
The proportional relationship between core displacement and output voltage is maintained correctly. Furthermore, since the magnetic flux density of the primary coil is strengthened by the ferromagnetic sub-core to which a high-frequency current is excited, the value of eddy current loss generated in the core is large, and therefore a large output voltage can be obtained. Especially for differential detectors with small coil widths and diameters, linearity can be maintained correctly and a drop in output voltage can be prevented.

Next, specific examples and comparative examples will be shown. A specific example uses a ring-shaped aluminum core with a sub-core of an iron rod fixed through a ring hole, and a comparative example uses a ring-shaped aluminum core and a rod-shaped iron core.

In the example below, the bobbin inner diameter, outer diameter, groove width,
The diameter of the bottom of the groove, the number of turns of the primary coil, the number of layers, the width of the winding,
The number of turns, excitation frequency, core material, outer diameter, inner diameter, and length of the secondary coil were changed.

The bobbin was made of plastic, and the distance between the two grooves was 2 mm. In all examples, the primary coil was a polyurethane wire with a diameter of 0.10 mm wound through two grooves in each bobbin, and a polyurethane wire of the same diameter was tightly wound on top of the secondary coil and wound separately in the two grooves. . The excitation current of the primary coil is a 1V sine fluid alternating current. The frequency used was selected to provide the best linearity (approximately 1 to 0.5% or less).

It was confirmed that each core maintains a nearly correct proportional relationship with the output voltage within the proportional range.

Since the diameter of the coil in Example 1 is larger than that in Example 2, the operating frequency is naturally lower. Also, in Example 1, the diameter of the core is
The aluminum core is large at 9.8 mm, so the output voltage of the aluminum core due to eddy current loss shown as a comparative example is higher than that of the iron core due to magnetic permeability, but in Example 2, the core diameter is small at 4 mm, so the aluminum core is It is lower than the core. However, in the case of the aluminum core with the iron sub-core of the present invention, it was confirmed that in both Examples 1 and 2, the output voltage was higher and the residual zero voltage was lower than when any of the above-mentioned cores was used.

(Example 1) Bobbin Outer diameter 15mm Inner diameter 10mm Groove width 3mm Groove bottom diameter 11mm Primary coil 165 times 4-layer winding Width 8mm Secondary coil 250 times (2 pieces) Operating frequency 150KC (1) Aluminum core Outer diameter 9.8mm Inner diameter 5mm Length 5mm Proportional range ±2mm Maximum output 1.05V Residual zero voltage 30mV or less (2) Iron core Outer diameter 9.8mm Round bar Length 5mm Proportional range ±2mm Maximum output 0.8V Residual zero voltage 50mV or less (3) This invention Core: Ring-shaped aluminum core, outer diameter 9.8mm, inner diameter 6mm
Length 5mm Iron sub-core Outer diameter 6mm Inner diameter 3.2mm Length 50mm Proportional range ±2mm Maximum output 1.3V Residual zero voltage 5mV or less (Example 2) Bobbin Outer diameter 8mm Inner diameter 4.2mm Groove width 3mm Groove bottom diameter 5mm Primary Coil 160 times 4-layer winding Winding width 8 mm Secondary coil 224 times (2 times) Operating frequency 300KC (1) Aluminum core Outer diameter 4 mm Inner diameter 3 mm Length 5 mm Proportional range ±2 mm Maximum output 0.65 V Residual zero voltage 35 mV or less (2) Iron core Outer diameter 4mm Round bar Length 5mm Proportional range ±2mm Maximum output 1V Residual zero voltage 50mV or less (3) Core of the invention Ring-shaped aluminum core Outer diameter 4mm Inner diameter 3mm Length 5mm Iron sub-core Outer diameter 3mm Round Rod length 50mm Proportional range ±2mm Maximum output 1.4V Residual zero voltage 10mV or less

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of one embodiment of the present invention, and FIG.
The figure is a perspective view of the bobbin of the same embodiment, Fig. 3 is a wiring diagram of the same embodiment, Fig. 4 is a diagram showing the relationship between core displacement and induced voltage, and Fig. 5 is a side view of another embodiment. Cross-sectional view. 1...Bobbin, 2,14...Hollow hole, 6...1
Secondary coil, 8, 9... Secondary coil, 12, 15...
... Core, 13, 17 ... Sub-core, 16 ... Support pipe.

Claims (1)

[Claims] 1. A core that moves according to the movement of the detected member, a primary coil that is arranged along the movement path of the core and is excited by alternating current, and a secondary coil that generates a voltage difference in proportion to the movement of the core. In ^a differential ^detector consisting of It is made of ferromagnetic rods or tubes with high magnetic permeability (specific magnetic permeability of about 10 ³ to 10 ⁶ ) that extend over the entire width, and are
A differential detector characterized by applying an excitation current of ~2MC) to the primary coil.