JPH02246301A - Elimination of residual magnetism of electromagnet - Google Patents

Abstract

PURPOSE:To realize the highly reliable releasing of an object to be attracted by detecting the magnetic flux density of a core with a magnetic sensor, and interrupting the current supply to a reverse exciting coil when residual magnetism vanishes. CONSTITUTION:When a contact 11 is opened, contacts 13a, 13b are opened, and contacts 14a, 14b are closed. Thus a current circuit to an inverse exciting coil 4 is formed, and inclined to make a current flow in the direction inverse to an arrow A. However, on account of the inverse electromotive force of a coil 4, a current in the arrow A direction flows in the closed circuit constituted of the coil 4 and a varistor 18 for a short period. When the current attenuates and becomes zero, an inverse exciting current, which is restricted lower than an ordinary value by a limiting resistor 15, begins to flow in the arrow B direction, and inverse exciting magnetic flux is applied to a core 2, so that the residual magnetism is gradually cancelled. When the residual magnetism becomes zero, this state is detected by a magnetic sensor 5 installed in the magnetic path of the core 2, and an operation coil Fx turns to the non-operation state. Hence a contact Fxa is opened, so that the contact 14a, 14b are opened, and the current flowing for reverse excitation is ended. As a result, the magnetic flux in the iron core 2 vanishes, and a work 25 is rapidly released, so that the reliability of releasing can also be increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to various devices using electromagnets, such as electromagnetic chucks, electromagnetic clutches, electromagnetic valves, etc.
The present invention relates to a method for removing magnetism remaining in an iron core when power to an attraction coil is cut off.

(Prior art) If there is residual magnetism as described above, the time for the object to be attracted (for example, the workpiece in an electromagnetic chuck, the armature air plate in an electromagnetic clutch, the movable plunger in an electromagnetic valve) to be released from the iron core may be delayed. In extreme cases, release may become impossible.For this reason, in the past, the residual magnetism was removed by passing reverse excitation current through a reverse excitation coil attached to the iron core for a predetermined period of time determined by a timer. This ensures smooth release of the adsorbed object.

[Problem to be solved by the invention]

However, with this conventional method for removing residual magnetism from electromagnets, if the power supply voltage for reverse excitation changes to high or low, or the temperature of the reverse excitation coil changes, the amount of current supplied to the reverse excitation coil may be too large or too low. This causes a problem in that reverse excitation becomes excessive or insufficient, and the ability to smoothly release the object to be attracted decreases.

The present invention has been made in view of the above points, and its purpose is not only to be able to remove residual magnetism by reverse excitation, but also to be able to eliminate residual magnetism due to changes in power supply voltage and coil temperature in the case of reverse excitation. To provide a method for removing residual magnetism from an electromagnet, by which de-excitation can be terminated after an appropriate amount of de-excitation has been performed, and the smooth release of an object to be attracted can be performed with high reliability. .

[Means to solve problems]

In order to achieve the above object, the present invention takes the measures as described in the claims above, and its effects are as follows.

[Effect]

After the attraction coil is energized, the reverse excitation coil is energized. The residual magnetism of the iron core gradually decreases due to the magnetic flux of reverse excitation generated by the energization.

When the magnetic sensor detects that the residual magnetism has become substantially zero, the energization termination means terminates energization of the reverse excitation coil.

〔Example〕

The drawings showing the embodiments of the present application will be described below.

In the electromagnet 1 shown in FIG. 1, reference numeral 2 denotes an iron core, for example, an E-shaped iron core consisting of a central magnetic pole 2a and yokes 2b, 2b on both sides thereof. Note that this may be a U-shaped, rod-shaped, or pot-shaped iron core.

3.3.3 shows an adsorption part in the iron core 2, which is composed of the end faces of the central magnetic pole 2a and the yoke 2b.

Reference numeral 4 denotes a coil disposed around the central position $12a, and 4a indicates its terminal.This coil 4 functions both as an attraction coil and as a reverse excitation coil by reversing the direction of energization as described later. The numeral 5 indicates a magnetic sensor interposed in the magnetic path of the center magnetic pole 2a, and is located within the magnetic gap 6 formed by cutting the center M1 cutout 2a. As the magnetic sensor 5, a magnetoresistive element is used in this example. 5a indicates a terminal of the magnetic sensor 5.

If the gap 6 is large, the excitation ampere turns of the coil 4 will increase, resulting in an increase in power consumption and a decrease in the adsorption force. Good (e.g. 0.5aaa degrees), 7
is a spacer made of a non-magnetic material disposed in the gap 6 at a location other than the location where the sensor 5 is present. This is to prevent the sensor 5 from being crushed by the magnetic attraction force of the parts on both sides separated by the gap in the central magnetic pole 2a,
It was used to mechanically integrate the parts on both sides. It should be noted that the magnetic sensor 5 may be provided at other locations within the magnetic path of the iron core 2, for example at locations indicated by symbols a and a.

Next, an energization control circuit 10 for controlling energization to the coil 4 of the electromagnet 1 will be explained based on FIG. The control circuit 10 includes an operating section, a suction M control section, a reverse excitation control section, and reverse excitation energization termination means. First, the operating section is composed of control contacts 11.

The contact 11 is opened and closed by external operation. The tiII control section is composed of the operating coil 12, 13 of the electromagnetic switch and the contacts 12al, 12bl, 13a, 13b operated by each of them.The zero-order reverse excitation control section is composed of the operating coil 14 and a contact 14a operated thereby;

The prayer is accomplished in 14b. 15 is a current limiting resistor for reverse excitation. The energization termination means for zero-order reverse excitation includes an electromagnetic switch 16 and a contact 76a operated by the electromagnetic switch 16, and a contact operated by an operating coil in an energization termination control circuit to be described later. It is composed of Fxa. Note that 13c and 14C are interlock contacts operated by coils 13 and 14, respectively, 16b is a self-holding contact operated by coil 16, 17 is a rectifier (unnecessary if DC Ttil is used), and 18 is a varistor for absorbing reverse voltage surge of the coil 4.

Next, the energization termination 11N1 circuit 20 for controlling the 1ffl energization termination means will be explained based on FIG. 2
1 is a conversion circuit. This is because the resistance value of the magnetoresistive element used as the magnetic sensor 5 changes only in accordance with the density of the magnetic flux applied to it as shown in FIG. The circuit was
A Brifuji circuit using resistors R1 and R2 is used, and the magnetoresistive element 5 is placed on one side thereof. In this example, the other resistors R1 and R2 constituting the Brifuji circuit are provided at a location away from the m1 stone 1, but they may also be provided in the gap 6 together with the sensor 5. 22 is an amplifier and an operational amplifier. is used. Fx is an operating coil for operating a contact point Fxa of the energization termination means, and 23 is a freewheeling diode.

Next, the control circuits 1O and 1ll11 are terminated by the control circuit 2.
The control of the electromagnet 1 by 0 will be explained based on FIG.

When contact 11 is closed at T1, contact 13a is closed by an operation that is easily understood from the circuit diagram of FIG.

13b is closed, and a normal excitation current flows through the coil 4 in the direction shown by arrow A in FIG. Then, magnetic flux Φ for attraction is applied to the iron core 2 by the coil 4 as shown in FIG. 1, and the workpiece 25 is attracted to the attraction portion 3.

The generation of the magnetic flux Φ is detected by the magnetoresistive element 5, turned into a voltage signal by the conversion circuit 21, and after being amplified, the operating coil Fx is operated (jiI]m). Therefore, in the circuit shown in FIG. The contact Fxa is closed, operating the coil 16, and the contact 16a is in a closed state.

When contact 11 is opened at T2, contact 13a opens, by operation that is easily understood from the circuit diagram of FIG.

13b opens and contacts 14a and 14b close. That is, a circuit for energizing the reverse excitation coil 4 is formed, and an attempt is made to cause current to flow through the coil 4 in the direction opposite to arrow A. However, due to the back electromotive force of the coil, a current in the direction of arrow A flows through the closed circuit of the coil 4 and the varistor 18 for a short time. Eventually, the current attenuates and becomes zero (Fig. 5 T
3, at this point there is residual magnetism in the iron core 2 as indicated by symbol a. ) Next, the above-mentioned closed contacts 14a, 14b
A current for reverse excitation in the direction shown by arrow B flows through the coil 4. This current is suppressed by the limiting resistor 15 to a smaller value than the normal excitation current. When the current for reverse excitation begins to flow, the magnetic flux for reverse excitation is applied to the iron core 2, so the residual magnetism is gradually canceled out by the magnetic flux for reverse excitation. When it becomes substantially zero, it is detected by the sensor 5 and the operating coil Fx shown in FIG. 3 becomes inactive. For this reason, in the circuit shown in FIG. 2, since the contact Fxa is opened, the contacts 14a and 1 are opened by an operation that can be easily understood from the circuit diagram.
4b is opened, and the supply of the current for reverse excitation is terminated.

The operations from T2 to T4 are reliably performed in an extremely short period of time, and the workpiece 25 is quickly released as the magnetic flux of the iron core 2 disappears.

The above-mentioned "substantially zero residual magnetism" means that the presence of a small amount of residual magnetism that does not adversely affect the work release itself or the time required for release as described above is acceptable. - The acceptable level of residual magnetism is generally 1710 to 1720 or less at the time of adsorption. Further, the control circuit shown in FIG. 2 can also be formed from a semiconductor circuit.

Next, FIG. 6 shows a connection method when using the Hall IC 27 as a magnetic sensor. Since a voltage signal corresponding to the magnetic flux density can be obtained from the Hall IC 27 as shown in FIG. 7, the amplifier 22 can be directly connected as shown in FIG.

Next, Figure 8 shows electromagnets with different core structures.
A main iron core 31 and an auxiliary iron core 3 in which iron cores 2e are arranged in parallel with each other.
An electromagnet (
For example, an example is shown in JP-A-63-134492. In the case of such an electromagnet, the magnetic sensor 5e may be provided in the main iron core 31 as shown in the figure (in addition to being provided in the auxiliary iron core 32 as shown by the imaginary line).

It should be noted that parts that are functionally the same or equivalent to those in the previous figure are given the same reference numerals as in the previous figure with an alpha bent e, and redundant explanations are omitted.

(Also, the same idea will be used in the next and subsequent ones, and the ``2g'' of Alpha Vent will be added in order, and the duplicate explanation will be omitted.) Next, in Fig. 9, an adsorption coil 35 is installed around the center magnetic pole 2af, Furthermore, this is an example of an electromagnet in which a reverse excitation coil 36 formed separately from the attraction coil 35 is provided around the outer periphery.* 35a and 36a indicate connection terminals.

like this! In the case of magnets, the number of contacts for controlling the energization of the coils 35 and 36 in the energization control circuit is one contact 13af, as shown in FIG.

14af is enough. Also, diodes 37 and 38 as shown in the figure can be used as surge absorbing elements.

Next, FIG. 11 shows an example in which an electromagnet having an iron core having the structure shown in FIG. 8 is provided with an independent attraction coil 35g and a reverse excitation coil 36g.

〔Effect of the invention〕

As described above, in the present invention, when the attraction of the object to be attracted is completed and the object to be attracted is released, the iron core 2 is reversely excited by energizing the reverse excitation coil to remove its residual magnetism. It has the advantage of allowing 25 to be released smoothly.

Furthermore, when reverse excitation is performed as described above, if the power supply voltage for reverse excitation changes to high or low, or the temperature of the reverse excitation coil rises and only a small current flows even with the same power supply voltage. Also, by detecting the magnetic flux density of the iron core 2 with the magnetic sensor 5, the energization to the reverse excitation coil can be stopped just when there is no residual magnetism. This has the effect of greatly increasing the reliability of smooth release of the adsorbed object 25.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, in which Fig. 1 is a schematic vertical cross-sectional view of an electromagnet, Fig. 2 is a circuit diagram of the energization control circuit, Fig. 3 is a circuit diagram of the energization termination control circuit, and Fig. 4 is a schematic diagram of the energization control circuit. Diagrams showing the properties of the magnetoresistive element, Figure 5 is a time chart for explaining the operation, Figure 6 is a time chart for explaining the operation.
Figure 7 shows the connection method when using a Hall IC, Figure 7 shows the properties of the Hall IC, Figure 8 is a schematic longitudinal section showing electromagnets with different core structures, and Figure 9 shows the respective A schematic vertical cross-sectional view of an electromagnet equipped with an independent attraction coil and a reverse excitation coil, FIG. 10 is a circuit diagram showing the main part of the energization control circuit used in the electromagnet of FIG. FIG. 2 is a schematic vertical cross-sectional view showing an example in which the electromagnet having the iron core structure shown in the figure is provided with an independent adsorption coil and a reverse excitation coil. 2... Iron core, 4... Coil (for adsorption and reverse excitation)
, 5... Magnetic sensor, 35... To Figure 1 for adsorption λ Figure 5 Figure 112 Figure 6 @ Figure 7 Magnetic flux fJa B Figure Figure 10 Figure O Figure 11

Claims (1)

[Claims] An iron core equipped with a suction part for attracting objects to be attracted is equipped with an adsorption coil for providing magnetic flux for adsorption to the iron core and a reverse excitation coil for providing magnetic flux for reverse excitation. In this method, the residual magnetism of the iron core is removed by the magnetic flux emitted from the reverse excitation coil by energizing the reverse excitation coil after the energization of the reverse excitation coil is completed. A magnetic sensor is interposed to detect the magnetic flux density of the magnetic path, and an energization termination means is connected to the circuit for energizing the reverse excitation coil, so that when the reverse excitation coil is energized, A method for removing residual magnetism from an electromagnet, characterized in that when the magnetic flux density detected by the magnetic sensor becomes substantially zero, energization to the reverse excitation coil is terminated by the energization termination means.