JPH04120707A - Excitation of lifting electromagnet - Google Patents

Abstract

PURPOSE:To dispense with operator's selective operation and to prevent danger due to the overload of a crane by detecting variations in a lifting target of a lifting electromagnet on the basis of variations in magnetic flux flowing through magnetic poles of the electromagnet and by selecting excitation patterns of the electromagnet from detection results so as to be as required. CONSTITUTION:The inward magnetic pole 8 of a lifting electromagnet is fitted with a search coil 9, and a fluxmeter 10, a voltage switching circuit 11, a signal generator 12 for forward excitation gate, and a reverse excitation signal generator 13 are provided. When steel susceptible to overlifting mixes in lifting targets and is attracted, it generates difference from these lifting materials and is detected through the fluxmeter 10 by variation in the induction power of the search coil 9 so as to automatically switch excitation patterns by the voltage switching circuit 11. Also it is so designed that upon ON command to the lifting electromagnet, excitation is made at a maximum voltage when the fluxmeter output is less than a prescribed value and excitation voltage is decreased when the fluxmeter output exceeds the prescribed value.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a lifting electromagnet mainly made of scrap iron materials, and a lifting electromagnet itself that selects an excitation pattern suitable for each of the various steel materials to be lifted. This invention relates to an improvement in the excitation method of a lifting electromagnet, which provides an over-hanging detection function to a lifting electromagnet.

[Prior Art] A conventional device was constructed as shown in FIG. 3(A). In the same figure (a), excitation coil 1 is a thyristor SCR for forward excitation, and thyristor 5CR2 is for reverse excitation.
This is an excitation device consisting of:

3 is a gate signal generator for forward and reverse excitation! , 4 is an AC power supply, and 5 is a power switch.

Reference numeral 6 denotes an excitation pattern changeover switch through which the crane operator visually observes the object to be lifted and selects the excitation pattern to be changed to an appropriate excitation pattern just before the object is attracted.

7 is a controller that turns on excitation coil 1.

This is for performing an OFF command operation.

Although not shown, a crane for lifting and moving the electromagnet is also installed separately.

Figure (B) is a characteristic diagram showing changes in the type and amount of lifting of the lifting electromagnet based on the object to be lifted.

[Problem to be solved by the invention] In the conventional lifting electromagnet for scrap iron materials, the bulk specific gravity (apparently the upper specific gravity) of the hanging steel material ranged from 0.5 to 4.0, so due to its structure, There were the following problems.

The lifting electromagnet is designed to have as large a capacity as possible so that it can lift a large amount of scrap iron material, which is difficult to lift with the scrap lifting electromagnet and the crane attached to it, and has a so-called low bulk specific gravity.

However, there are times when scrap iron materials with large bulk specific gravity, such as pig iron and scrap steel chips, are hoisted together with these scrap iron materials.

In such a case, if the electromagnet is excited with a high voltage, the lifting amount will increase, and there is a risk that the crane capacity will be exceeded due to the relationship: crane capacity ≧ dead weight of the lifting electromagnet + lifting amount.

Therefore, in the past, the load was detected by a weighing machine while lifting, and if this load exceeded the predetermined lifting amount, an overload alarm was generated, and the operator reduced the excitation voltage to prevent the lifted object from being lifted. Adjustments were also made by dropping a part of the
It was still practiced to operate visually without using a weighing machine.

However, as described above, if cargo is handled in excess of the crane's capacity, the strength of the girder of the crane may be insufficient or the single hoisting motor may be overloaded, resulting in failure.

An object of the present invention is to provide a method for exciting a lifting electromagnet that solves the above-mentioned problems of the conventional method.

[Means for Solving the Problems] The present invention provides a lifting electromagnet that is equipped with a plurality of types of excitation patterns as excitation means depending on the object to be lifted by the lifting electromagnet, in which a change in the object to be lifted each time by the lifting electromagnet is A method of excitation of a lifting electromagnet is developed, in which a change in the magnetic flux flowing through the magnetic poles of the electromagnet is detected, and the excitation pattern of the electromagnet is selected to be a desired pattern based on the detection result.

[Example] The present invention will be specifically explained below using an example shown in FIGS. 1 and 2. In each of these figures, the same reference numerals as in FIG. 3(a) are used to indicate structures equivalent to the conventional ones.

As shown in FIG.
A search coil 9 is attached to the magnetic flux meter 10. as shown in FIG. Voltage switching circuit 11. Signal generator for positive excitation gate 12. A reverse excitation signal generator 13 is provided.

In this case, the search coil 9 is, for example, 1.5 m.
A conductor wire of approximately mφ may be wound around the magnetic pole 8 in 5 to 10 turns.

With this search coil 9, for example, among the objects to be lifted,
When steel materials that tend to be over-suspended, such as thick steel plate scraps, are mixed and adsorbed, a difference will occur between these materials, and this will cause a difference in magnetic flux change caused by a change in the electromotive force of the search coil 9. is detected via the magnetometer 10, and the excitation pattern is automatically switched (voltage drop) by the voltage switching circuit 11.

Note that 14 is a coil holder.

Further, in the device of the present invention, when an ON command is given to the lifting electromagnet, if the magnetometer output is below a specified value, it is excited at the maximum voltage, and if the magnetometer output exceeds the specified value, the excitation voltage is lowered.

Here, the specified value of the magnetometer output is set each time according to the type of steel material handled by the user and the limited lifting amount depending on the crane capacity.

And, there is a method of changing the amount of decrease in excitation voltage in stages,
There are various methods such as a method of controlling the firing angle of the thyristor steplessly.

[Function] In the above configuration, when lifting various scrap iron materials by the lifting electromagnet 1 In the present invention, when iron materials are attracted, the search coil 9 changes the object to be attracted each time by the induced electromotive force of the coil 9. Detection based on magnetic flux changes.

Based on this detected amount, the voltage switching port Ill automatically switches to an appropriate excitation pattern.

Therefore, the amount of iron material to be hoisted is always appropriate for the capacity of the hoisting electromagnet and the crane, and dangers such as breakdown of the crane etc. are now prevented.

[Effects of the Invention] The present invention provides an excitation method for a lifting electromagnet in which the lifting amount, which is the limit of the crane capacity, is constantly detected by changes in magnetic flux when adsorbing iron materials, and the excitation pattern can be selected as required. Although.

It has the following excellent effects.

■There is no need for the operator to make a selection operation even when there are many types of scrap.

■Lifting amount is limited regardless of the cold or hot state of the lifting electromagnet, preventing danger from overloading the crane.

■No need for crane overload inspection equipment (load cell, weighing machine). Therefore, it is possible to respond to the Labor Standards Bureau's safety concerns.

■Since it is possible to automatically remove scraps with large bulk specific gravity that are sometimes lifted, it is possible to make the electromagnet large (self-heavy) by lifting mainly general scrap (those with small bulk specific gravity).

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention. FIG. 1 is a sectional view of the lifting electromagnet itself, and FIG. 2 is a circuit diagram showing its configuration in a single line diagram. FIG. 3(A) shows a conventional example, and FIG. 3(B) is a chart showing the relationship between scrap type and lifting amount in a certain lifting electromagnet. 1: Excitation coil of lifting electromagnet 2: Excitation device 9 Search coil 10, magnetometer 11, voltage switching circuit 12, gate signal generator for positive excitation

Claims (1)

[Claims] 1. In a lifting electromagnet equipped with a plurality of types of excitation patterns as excitation means depending on the object to be lifted by the lifting electromagnet, a change in the object to be lifted each time by the lifting electromagnet is detected based on a change in magnetic flux flowing through the magnetic poles of the electromagnet. A method for excitation of a lifting electromagnet, characterized in that the excitation pattern of the electromagnet is selected to be a desired one based on the detection result.