JPS6211310B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a pulse demagnetizer for a tachometer, which demagnetizes a rotating magnet of a tachometer such as an automobile speedometer or tachometer, and in particular, it is designed to eliminate so-called hiss reduction. This is what I did.

BACKGROUND TECHNOLOGY AND PROBLEMS In speedometers and tachometers as accessories for automobiles, as shown in FIGS. 1 and 2, a rotating magnet 1 is rotated to cause an eddy current to flow through a guide plate 2.
A torque is generated on the guide plate 2 based on the Coulomb force between the two, and the pointer 3 is caused to swing in accordance with this torque. That is, a rotating shaft 5 is guided in the frame 4, and a rotating magnet 1 and a yoke 6 are integrally attached to the driving end of the rotating shaft 5.
A part of the guide plate 2 is disposed in the gap between the yoke 6 and the rotating magnet 1, and the pointer 3 rotates together with the guide plate 2. This rotation is biased by the hairspring 7.
The rotating magnet 1 and the yoke 6 rotate together with the rotating shaft 5. In this case, the magnetic flux returning from the yoke 6 to the rotating magnet 1 generates an eddy current in the guide plate 2, and this eddy current causes the guide plate 2 to rotate. It is designed to receive torque corresponding to the rotation of the rotating shaft 5. The pointer 3 swings by a predetermined angle in accordance with this torque. Note that an indicator board 8 is provided on the front surface of the frame 4, and the rotation of the rotating shaft 5 can be read from the scale of the indicator board 4.

By the way, in such tachometers such as speedometers and tachometers, we magnetize the rotating magnet 1 to the saturation magnetic flux density, and then use a pulse demagnetizer to demagnetize it to the desired state of magnetization, so that the rotation and scale match. Adjust the sensitivity accordingly. That is, as shown in FIG. 3, a tachometer M, especially its yoke 6, is placed between the gaps of the demagnetizing yoke 9, and a pulsed demagnetizing current as shown in FIG. 4 is supplied to the demagnetizing coil 10. be. The pulse demagnetizing power supply 11 is for generating the current shown in FIG.

As can be understood from Figure 4, the pulse demagnetizing current gradually increases, and along with this, the amount of demagnetization increases and eventually the desired sensitivity adjustment can be performed. Become. Of course, since the rotating magnet 1 rotates, such pulse demagnetizing current is not necessarily formed in the direction that demagnetizes the rotating magnet 1, but may be formed in the direction that demagnetizes the rotating magnet 1. , may also be formed in the opposite direction. However, if it is formed in the opposite direction, that is, in the direction of magnetization, it simply acts as a dummy and does not affect demagnetization in any way. In short, the demagnetization efficiency only deteriorates by the amount of the dummy. In order to demagnetize efficiently, pulses may be supplied in synchronization with the rotation of the rotating magnet 1.

However, in such demagnetization operations, a phenomenon generally called hiss is known. That is, it is assumed that a desired rotation is given to the rotating shaft 5. It is assumed that the pointer 3 is initially at the position shown by C in FIG. 3, and that it is gradually swung counterclockwise by demagnetization. In this case, when a pulsed demagnetizing current is supplied, the magnet oscillates considerably in the counterclockwise direction, and then returns slightly at pulse intervals. Furthermore, when demagnetization is continued until the final adjustment point, point B, and the pulse demagnetizing current is stopped, a phenomenon occurs in which the pointer returns from point B to point A.

If there is such a hiss, the pointer will vibrate and slowly swing counterclockwise, causing it to go back a little after adjustment, making it extremely complicated to make adjustments by anticipating such errors. It was hot. Such hiss is caused by the fact that when a demagnetizing magnetic field is formed in the demagnetizing yoke 6, not only magnetization but also magnetic flux is generated by this magnetic field, whereas when the demagnetizing magnetic field is removed, only the amount of magnetization is generated. This is thought to be due to the fact that .

Moreover, the above-mentioned hiss is thought to be caused by demagnetization by a direct current magnetic field.
Therefore, it is thought that such hiss will be reduced if a demagnetizing magnetic field is formed using an oscillating current. Therefore, it has been proposed to supply a demagnetizing current to the demagnetizing coil 10 using a circuit as shown in FIG. That is, in FIG. 5, a commercial power source and a thyristor circuit (both not shown) whose conduction angle is controlled are arranged on the primary coil 12a side of the transformer 12, and a rectifier diode 13 is arranged at one end of the secondary coil 12b.
One end of a capacitor 14 is connected to the cathode of this diode 13, and the other end of the capacitor 14 is connected to the other end of the secondary coil 12b. The anode of a thyristor 15 is connected to the cathode of the diode 13, and one end of the demagnetizing coil 10 is connected to the cathode. The other end of the demagnetizing coil 10 is connected to the other end of the capacitor 14. A diode 17 is connected in parallel to the anode/cathode path of the thyristor 15.

In such a configuration, the capacitor 14 is charged with a voltage set by the thyristor circuit on the primary side, and then by turning on the thyristor 15, a current having the oscillating waveform shown in FIG. 6 is supplied to the demagnetizing coil 10. be done. A vibration waveform is intermittently generated by the vibration system of the capacitor 14 and the demagnetizing coil 10 to form a demagnetizing magnetic field. This is shown in FIG. As can be understood from FIG. 7, the voltage currently charged in the capacitor 14 gradually increases depending on the conduction angle setting of the primary side thyristor circuit, and therefore the amount of demagnetization gradually increases. go. This operation is then stopped when the desired amount of demagnetization has been achieved.

However, with such a waveform of demagnetizing current,
As expected, hiss remained. This is thought to be due to the fact that the integral value of the waveform shown in FIG. 6 remains as a DC component, which causes the pointer to return after the demagnetizing magnetic field is removed.

Purpose of the Invention The present invention has been made in consideration of the above circumstances, and its object is to provide a pulse demagnetizer for a tachometer that can accurately perform demagnetization operations without the so-called hiss phenomenon. .

Summary of the Invention In order to achieve the above object, the present invention connects a series circuit of a resistor and a diode in parallel to a coil for passing current through the demagnetizing coil. After a demagnetizing current with a high peak value is supplied to the demagnetizing coil, a current with a low peak value is supplied to the demagnetizing coil in the opposite direction. That is, the current in the reverse direction is reduced by a series circuit of a resistor and a diode. The peak value of the current in the reverse direction is preferably 10 to 30% of the initial demagnetizing current.
shall belong to.

In this invention, by supplying a current in the opposite direction with a smaller peak value than the demagnetizing current, the pulsed demagnetizing current pulls back the pointer that is about to swing beyond the amount of magnetization, thereby reducing hiss. can be done.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings from FIG. 8 onwards.

FIG. 8 shows the main part of this embodiment. Furthermore, this 8th
In the figure, parts corresponding to those in FIG. 5 are designated by corresponding reference numerals, and detailed explanation thereof will be omitted.

In the example shown in FIG. 8, a series circuit of a resistor 21 and a diode 22 is connected in parallel to the capacitor 14. Regarding the direction of the diode 22, the anode of the diode 22 is connected to the capacitor 14.
so that it is on the ground side. That is, the current passing through the rectifier diode 13 does not flow through the diode 22, so that the capacitor 14 is reliably charged.

In such a configuration, after the capacitor 14 is charged with a predetermined voltage, a trigger pulse is supplied to the gate of the thyristor 15 to turn it on. Then, a current as shown in FIG. 9 will flow through the demagnetizing coil 10. That is, time t ₀ after turn-on
The capacitor 14 is discharged from t1 to _t1 , and when the capacitor 14 is finally discharged at time _t1 ,
Thereafter, current will flow in the same direction due to the inductance of the demagnetizing coil 10. At this time, the diode 22 is turned on because it is in the forward direction of the current, and a detour consisting of a series circuit of the resistor 21 and the diode 22 is formed with respect to the capacitor 14. Therefore, the amount of charge in the capacitor 14 decreases between time t ₁ and time t ₂ . Eventually, the charging of the capacitor 14 ends and it begins to discharge, but since the energy stored in the capacitor 14 is small, the next current in the reverse direction will be extremely small compared to the above-mentioned pulsed current. Moreover, the capacitor 14 is discharged also through the series circuit of the diode 22 and the resistor 21, and as a result, the reverse current flowing through the demagnetizing coil 10 from time _t2 to time _t3 becomes small.
To put it simply, the current in the direction opposite to the demagnetization direction that continues with the current in the demagnetization direction becomes extremely small due to the damping of the diode 22 and the resistor 21.

Of course, such a pulsed vibration waveform is intermittently supplied to the demagnetizing coil 10 as shown in FIG. 10, and its peak value gradually increases.

When such a pulse is supplied to the tachometer, a demagnetizing magnetic field is formed by the pulsed current (current from time _t0 to _t2 in FIG. 9), and the rotating magnet is gradually demagnetized. Of course, this pulsed current creates a magnetic field, and this magnetic field tends to cause the pointer to swing excessively. This is the cause of the hiss phenomenon as described above. However, there is a response time for the deflection of the pointer due to such a magnetic field, and this is caused by mechanical inductance components such as the mass of the guide plate 2, hairspring 7, and pointer 3 (see FIG. 2). Therefore, the pointer 3 does not rise sufficiently during this pulse current, and is eventually returned to its pre-response state by a pulse in the opposite direction. Therefore, the pointer 3 does not swing too much unnecessarily, and the phenomenon of hiss is avoided.

It is also possible to supply the demagnetizing coil with an AC waveform whose amplitude gradually increases as shown in Figure 11, but in this case as well, a DC component due to the integral value remains, similar to the vibration waveform in Figure 6. There is a phenomenon of hiss.

Effects of the Invention As explained above, according to the present invention, after a pulsed demagnetizing current is supplied, a current with a small peak value in the opposite direction is supplied, thereby eliminating the excess vibration caused by the demagnetizing magnetic field. can be pulled back to avoid the hiss phenomenon. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit thereof.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of a tachometer, Fig. 2 is a similar sectional view, Fig. 3 is a schematic diagram for explaining an example of a pulse demagnetizer for a tachometer, and Fig. 4 is a third example. FIG. 5 is a circuit diagram for explaining the circuit section of another pulse demagnetizer for a tachometer. FIG. 6 is a time chart for explaining the circuit example of FIG. 5. The figure also shows a similar time chart, and FIG. 8 is a circuit diagram showing an embodiment of the present invention.
9 and 10 are time charts for explaining the above embodiment, and FIG. 11 is a time chart for explaining a comparative example of the above embodiment. 1 is a rotating magnet, 2 is a guide plate, 3 is a pointer, 9 is a demagnetizing yoke, 10 is a demagnetizing coil, 14 is a capacitor, 15 is a thyristor, 21 is a resistor, and 22 is a diode.

Claims (1)

[Claims] 1. While the rotating magnet of the tachometer is rotating, a magnetic field for demagnetization is applied to the rotating magnet intermittently until the rotation of the rotating magnet applies appropriate torque to the induction body and the pointer swings to the appropriate angular position. In a pulse demagnetizer for a tachometer that applies , there is a coil that forms a magnetic field for demagnetization, a capacitor that is charged in the initial state with a voltage that causes a current in the demagnetizing direction to flow through the coil, and a capacitor that is charged in the above-mentioned state. A tachometer comprising a switching circuit for supplying current to a coil, and a series circuit of a diode and a resistor connected in parallel to the capacitor, the diode being reverse biased with respect to the initial charging voltage of the capacitor. Pulse demagnetizer for use.