JPH0362640B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an electric hoist such as an electric hoist, and particularly to a brake circuit thereof. [Background of the Invention] In general, electric hoisting machines need to be able to stop at any position during hoisting and lowering operations, and the suspended load must be held so that it does not fall, so a brake device is required. is attached. This brake device is designed to apply the brakes at the same time as the power to the drive motor is turned off. FIG. 1 generally shows the structure of an electric chain hoist. At the same time that voltage is applied to the drive motor 1, the electromagnet 2 is energized and the brake 3 is released. And the rotational force of the drive motor 1 is
The speed is reduced by the gear train of the reduction mechanism 4, and the reduced power is transmitted to the load sheave 5, which winds up or unwinds the link chain 6 that meshes with the load sheave 5, thereby hoisting or unwinding the hoist 7. Unwinding is performed. The operating lever 9 of the limit switch 8, which prevents over-winding and over-winding, is connected to the load sheave 5.
The mechanism is such that the angle is turned by a hanger 7 and a stopper 10, which are provided below the link chain and attached to both ends of the link chain, to turn off the power circuit and prevent over-winding or over-lowering. The brake of an electric chain hoist having such a structure has important components for the purpose of holding the load and preventing slips due to inertia. FIG. 2 is a sectional view showing the structure of the electromagnetic brake.
The friction plate 12 is fitted to the first stage pinion 13 by a spline or the like. When the electromagnet 14 is not energized, force is applied to the suction plate 16 by the push spring 15, and the frictional force generated between the friction plate 12, the suction plate 16, and the base 17 generates torque. Now, when the electromagnet 14 is energized, the suction plate 16 overcomes the spring force and is attracted to the electromagnet 14, the frictional force is released, the brake is released, and the electric chain hoist can be operated. There are two types of electromagnet 14: an alternating current type and a direct current type, and the former has the following disadvantages and advantages. Disadvantages of Γ AC electromagnets (1) They must be manufactured from laminated plates, which makes them expensive. (2) The laminated cores are manufactured by crimping them with rivets, etc., so they are susceptible to brake suction, impact when released, etc. The lifespan is short due to damage to the rivets. (3) Since a current of 4 to 5 times the rated current flows during startup, it is easy to burn out due to frequent use. Advantages of Γ AC electromagnets (1) Good response. That is, the electromagnetic force disappears at the same time as the power is turned on and off. In contrast, DC electromagnets have the following advantages and disadvantages. Advantages of Γ DC electromagnets (1) Electromagnets can be manufactured from iron plates or cast iron without using laminated plates, so they are inexpensive. (2) From the above, it is easy to ensure sufficient strength against impacts and have a long life. (3) It can generate twice the suction force of an AC type with the same suction area, so it can be made smaller. (4) Since a large starting current does not flow during startup, it is more resistant to high frequencies than AC type. Disadvantages of Γ DC electromagnets (1) When the power is cut off, the coil current has a delay time and decreases, and the residual magnetism is large and the response is poor. As mentioned above, each has advantages and disadvantages, but in the case of brakes for hoisting machines, torque is always applied in the lowering direction due to the gravitational speed of the suspended load, so the brake must stop during the lowering operation. In this case, if the brake response is poor, due to the gravitational acceleration,
Increases speed and causes a large descent distance. Therefore, AC type electromagnetic brakes are often used as brakes for hoisting machines, but they are not as good as DC types in terms of lifespan and frequent use. In order to take advantage of the advantages of using DC electromagnets as brakes for hoisting machines, the following conventional techniques have been used. In order to improve responsiveness, especially to prevent residual magnetism, it is common to install a shield plate 19 between the electromagnet 14 and the attraction plate 16, but this is not a fundamental solution as it also reduces the attraction force. . FIG. 3 is a diagram qualitatively showing the braking characteristics of the brake when the lowering is stopped. In other words, in Fig. 3, when the power is cut off at t ₀ , if there is a response delay until t ₁ , the motor speed increases from synchronous rotation speed ω ₀ to ω ₁ due to the load torque during that time, and then the braking force increases. added and braked. The descending distance of the load during that period corresponds to the area surrounded by the braking curve between t ₀ and _{t 2} and the time axis. Figure 4 is a drawing that qualitatively shows the braking characteristics of the brake at a lowering stop when the delay time is small, but compared to the case of the previous Figure 3, the above area is about 1/3 ing. In other words, in the case of brakes for hoisting machines, the brake operation delay time is more important than the brake torque itself.
It can be said that it has a large effect on the coasting descent distance of the fall. If you increase the braking force of the brakes and try to suppress this descending distance, the braking curve will become as shown by the broken line in Figure 3, and not only will you not be able to obtain a sufficient effect, but you will be forced to stop suddenly. As a result, an excessive impact force is applied to the hoisting machine, resulting in a dangerous situation. As described above, since the brake for a hoisting machine is subject to gravitational acceleration, it is essential that the brake has better responsiveness than a general brake. FIG. 5 is a general electrical circuit diagram of an electric hoist. The operation is performed by turning on the upper push button switch 26a, for example, to turn on the electromagnetic switch 20.
The coil 25a of a is excited, the contact of the lifting electromagnetic switch 20a is closed, the circuit of the brake 23 is closed, and the brake is released.
The driving electric motor 22 is rotated in the upward direction. The operation circuit generally uses a step-down transformer 24 to prevent electric shock and the like. When using a DC electromagnet for the brake, a circuit shown in FIG. 6 is generally used to obtain DC from an AC power source. That is, the rectification is half-wave rectification. This means that the attraction force of a DC electromagnet is proportional to the attraction area and ampere turns, but when obtaining the same ampere turns,
When the DC voltage doubles, the number of coil turns doubles and the coil wire diameter becomes 1/√2. In other words, it is necessary to wind a large number of thin wires, which is disadvantageous in manufacturing. For this reason,
Generally, half-wave rectification is used instead of full-wave rectification. The current half-wave rectified by the rectifying diode 27 has a waveform as shown in FIG. 8, which is close to alternating current, and therefore generates a beat when attracted. To deal with this, a commutation diode 29 is inserted in parallel with the brake coil. By inserting the commutation diode 29, the current shown in Fig. 9 flows, and as a result, the current shown in Fig. 9 flows through the brake coil 28, resulting in a slightly smoothed current waveform, which prevents humming during adsorption. At the same time, since the effective value can be increased, it produces the effect of increasing the suction force. Furthermore, since the brake coil has high inductance and generates a large surge voltage when the power is turned on and off, a surge absorber 30 such as a varistor is inserted in parallel with the brake coil to protect the diode from this surge. do. There are various methods for configuring a hoisting machine brake using a brake circuit having such a basic circuit configuration, but the following methods have been mainly used in the prior art. Examples of circuits according to the prior art are shown in FIGS. 10 to 12. In FIG. 10, the brake circuit 31 is connected directly to the hoisting motor 22 in parallel. In the case of this circuit, one end of the brake circuit is connected in front of the electromagnetic switch 32 to prevent the formation of a circuit in order to prevent a delay in response due to current flowing through the brake circuit due to the power generation effect caused by acceleration during braking of the hoisting motor. However, using the shielding plate 19 described above,
When braking during rated load hoisting operation, there is an operation delay of about 0.07 to 0.1 seconds, which is at a level that makes it impossible to use as a brake for electric hoisting machines. FIG. 11 shows what is called a quick cut circuit, in which the DC side of the brake circuit is cut off by an electromagnetic switch 33 for operating the electric motor, which has one additional contact. Furthermore, in order to eliminate the influence of the power generation action of the electric motor mentioned above, one phase on the AC side is connected to the electromagnetic switch 33.
is connected to the power supply side to prevent the formation of a circuit. In this case, since the DC side is cut off, it is affected by some transient phenomenon, but under the same conditions as above, the delay time is reduced to about 0.01 to 0.02 seconds, and it can be used as a brake for hoisting machines. be. FIG. 11 shows a circuit based on the same concept as FIG. 10, but in order to provide versatility, an AC relay is added instead of an electromagnetic switch, and the relay coil 34 is cut off by a contact point of the electromagnetic switch 32. The relay contact 35 is used to cut off the brake DC circuit. In this conventional example as well, under the same conditions as above, the operation delay is 0.01 to 0.02 seconds, and it can be used as a brake for a hoisting machine. As mentioned above, brakes for hoisting machines that use DC electromagnets require the addition of electromagnetic switch contacts and relays in order to reduce operation delays, which makes them expensive, so they are not suitable for high-frequency use. The advantages of not using a laminated core, such as high reliability, could not be taken advantage of. [Object of the Invention] An object of the present invention is to provide an inexpensive DC electromagnetic brake that has sufficient responsiveness as a brake for a hoisting machine. [Summary of the Invention] In order to achieve this object, the present invention utilizes only an existing electromagnetic switch (3 contacts) to configure a quick-cut circuit without adding any relays or contacts, and instead of commutating diodes. The key point of the present invention is that the circuit is formed only when energized. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG. 13. FIG. 13 is a partial diagram of an electric circuit of an electric hoist using the brake circuit according to the present invention. One end A side of the brake coil 28 is connected to the power source side of the electromagnetic switch 32. The cathodes of a rectifier diode 27 and a commutation diode 29 are connected to the other end B side, and the anode side of the rectifier diode 27 is in a different phase from the brake coil, and the anode side of the commutator diode 29 is in the same phase as the brake coil. are connected to the motor 22 side of the electromagnetic switch 32, respectively. Further, a surge absorber 30 is inserted in parallel with the brake coil for the purpose of absorbing surges generated from the brake coil 28. The operation of the brake circuit having the above configuration will be explained. At the same time as the electromagnetic switch 32 closes, the anode side of the commutation diode 29 connects to the brake coil 28.
It is short-circuited to the A side of the circuit, resulting in the circuit shown in FIG. In other words, it is equivalent to a basic brake circuit. When the electromagnetic switch 32 is opened, the circuits of the rectifying diode 27 and the commutating diode 29 are cut off almost simultaneously, so that all circuits except the surge absorber 30 are opened. In general, a surge absorber is an element that can only flow high voltage, and it can be considered as an open circuit because it has infinite resistance to the attraction voltage of the brake electromagnet. That is, since all the circuits to the brake coil are opened at the same time as the electromagnetic switch contacts are opened, the potential at both ends of the brake coil immediately becomes equal to or lower than the release voltage, making it possible to obtain extremely good responsiveness. Comparing and summarizing the response time of the brake circuit described in the prior art and the brake according to the present invention, the first result is
It will look like Figure 5. Figure 15 shows the operation delay time t ₀ measured under the same conditions for the brake response time, but when the circuit according to the present invention is used (the circuit in Figure 13), a relay or contact is added. A response time equivalent to that in FIG. 11 or 12 is obtained, and it can be used satisfactorily for a hoisting machine.

[Table] [Effects of the Invention] As described above, according to the present invention, the contacts of the existing electromagnetic switch can be used without adding any contacts or relays to the DC electromagnetic brake circuit.
Since the responsiveness of the brake can be improved, it is possible to provide an economical, highly reliable, and long-life electromagnetic brake for hoisting machines.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the structure of an electric chain hoist, Fig. 2 is a sectional view of an electromagnetic brake, Figs. 3 and 4 are graphs showing qualitative braking characteristics,
Figure 5 is a general electric circuit diagram of a hoisting machine, Figure 6 is a general rectifier circuit diagram of a DC electromagnet, Figures 7 and 8
Figure 9 is a current waveform diagram of each part flowing through the rectifier circuit, Figure 10 is an electric circuit diagram of the brake circuit, and Figure 1
1 and 12 are early cutting brake circuit diagrams according to the prior art, FIG. 13 is a brake circuit diagram according to the present invention, FIG. 14 is an electric circuit diagram showing the operation of FIG. 13, and FIG. 15 is a diagram of the response time. It is a comparison diagram. 1... Electric motor, 2... Electromagnet, 3... Electromagnetic brake, 4... Reduction mechanism, 5... Sprocket, 6
...Chain, 7 ... Hanging device, 8 ... Limit switch, 9 ... Limit lever, 10 ... Chain stopper, 11 ... Push button switch, 12 ... Friction plate, 13 ... 1st stage pinion, 14 ... Electromagnet, 1
5... Pressing spring, 16... Suction plate, 17... Base, 18... Pin, 19... Shielding plate, 20a...
... Electromagnetic switch for hoisting, 20b... Electromagnetic switch for lowering, 21a... Limit switch for hoisting, 2
1b... Limit switch for lowering, 22... Electric motor, 23... Brake, 24... Transformer, 25
a... Electromagnetic switch coil for hoisting, 25b... Electromagnetic switch coil for hoisting down, 26a... Push button switch for hoisting, 26b... Push button switch for hoisting down, 27
... Rectifier diode, 28 ... Brake coil,
29... Commutation diode, 30... Surge killer, 31... Brake circuit, 32... Electromagnetic switch (3 contacts), 33... Electromagnetic switch (4 contacts),
34... Relay coil, 35... Relay contact.

Claims (1)

[Claims] 1. In a DC electromagnetic brake consisting of a brake coil, a surge absorber and a commutation diode inserted in series with the brake coil, and a rectifier diode inserted in series with the brake coil, the above-mentioned A brake circuit for an electric hoist, characterized in that a rectifier diode circuit and a commutation diode circuit are turned on and off.