JPH028558Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a dynamic braking device applied to a series-wound motor in which a field and an armature are connected in series.

(Prior Art) In series-wound motors such as universal motors, dynamic braking is widely used in which the armature is disconnected from the power source to form a closed circuit for braking. This type of conventional device generally uses a plurality of electromagnetic contactors that switch circuits depending on driving and braking. As a result, the entire device becomes complicated, the number of parts increases, and the device becomes larger.

(Purpose of the invention) The present invention was devised in view of the above circumstances, and the purpose is to provide a dynamic braking device for a series motor that has a simple configuration, has a reduced number of parts, and is suitable for downsizing. do.

(Structure of the invention) In order to achieve this objective, the present invention utilizes a positive characteristic heat-sensitive resistance circuit whose resistance value rapidly increases as the temperature rises due to self-heating. That is, it includes an operating switch connected in series to a field and an armature, a positive temperature sensitive resistance circuit connected in parallel to the operating switch, and a braking switch forming a closed circuit together with the armature. The brake switch can be selectively closed.

(Example) The present invention will be described in detail below based on an example shown in the drawings.

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to a universal motor, where 10 is a field and 12 is an armature. 14 is a switch having a normally open contact 14a as a driving switch and a normally closed contact 14b as a braking switch. The normally open contact 14a is connected between the field 10 and the armature 12, and their series circuit together with the power switch 16 and the AC power source 18 form a closed circuit. Further, the normally closed contact 14b forms a closed circuit with the armature 12.

Reference numeral 20 denotes a PTC heat-sensitive resistance circuit, which is composed of a series circuit of a PTC heat-sensitive resistance element 22 and a resistor 24, and this circuit 20 has a normally open contact 14a connected in parallel. The PTC heat-sensitive resistance element 22 has a low resistance value near normal temperature, and when energized, the resistance value rapidly increases (approximately 1000 times) due to self-heating.
Temperature Characteristic) These are known as thermistors (product name), posistors (product name), etc.

In this embodiment, if the power switch 16 is first closed and the switch 14 is pressed at the same time, the normally closed contact 14b is opened and the normally open contact 14a is closed. Therefore, the armature 12 rotates. During this time, no current flows through the PTC heat-sensitive resistance element 22, so no self-heating occurs and the resistance value becomes low.

When the switch 14 is returned, the normally open contact 14a opens and the normally closed contact 14b closes. Therefore, while current flows through the field 10 and the armature 12 via the element 22 and the resistor 24, the armature 12 is short-circuited. As a result, a strong braking force is generated in the armature 12. The element 22 then heats up due to self-heating for several seconds, and its resistance value increases rapidly. Therefore, field 1
The zero current also decreases and the braking force becomes gradually weaker.

To restart, just press the switch 14. At this time, the element 22 cools down in a few seconds, and at the beginning of the next braking, a large field current flows again, making it possible to obtain a strong braking force.

In this embodiment, the field 10 may be provided at other positions, for example at the position 10a shown in phantom lines.

Furthermore, if the PTC heat-sensitive resistance element 22 has an appropriate resistance value at low temperatures, the resistor 24 may be omitted.

Furthermore, if a plurality of series circuits of resistance elements 22 and resistances 24 are prepared, and these are connected in parallel to the normally open contact 14a (see virtual line), and each resistance element 22 has a different temperature-resistance change characteristic, During braking, the resistance value of each resistance element 22 increases rapidly in turn. As a result, as the speed decreases, the resistance value of the positive characteristic heat-sensitive resistance circuit 20 is changed stepwise, and the field current is changed stepwise, thereby making it possible to smoothly change the braking force.

FIG. 2 is a circuit diagram of another embodiment.
The circuit shown in the figure is used to enable forward and reverse rotation. That is, in addition to the forward rotation switch 14, a reverse rotation switch 30 is provided, and the normally open contact 30a of this switch 30 is connected to a positive characteristic heat sensitive resistance circuit 3 for braking during reverse rotation.
2 were connected in parallel. Note that the normally open contact 30a of the switch 30 can be used as an operating switch, and the normally closed contact 30a can also be used as an operation switch.
b functions as a brake switch.

According to this embodiment, forward rotation and braking can be easily performed by operating the switch 14, and reverse rotation and braking can be easily performed by operating the switch 30, making it ideal for traveling cranes, winches, hoists, etc. that can frequently perform forward and reverse rotations. It can be a device.

It goes without saying that the present invention is applicable not only to motors using an AC power source but also to series-wound motors using a DC power source, and a changeover switch may be provided to flow the field current in the opposite direction during braking.

(Effects of the invention) As described above, the present invention connects a positive temperature sensitive resistance circuit in parallel to the operating switch connected in series to the field and the armature, and also provides a braking switch that closes the armature. Since the brake switch is configured to be able to selectively close the circuit, it is possible to perform dynamic braking with a simple configuration and a small number of parts without using a plurality of electromagnetic contactors. Moreover, the effect that the device can be made smaller can also be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is a circuit diagram of another embodiment. 10... Field, 12... Armature, 14a, 30
a... Normally open contact as an operation switch, 14b,
30b...Normally closed contact as a brake switch, 2
0,32... Positive characteristic heat sensitive resistance circuit.

Claims (1)

[Claims for Utility Model Registration] (1) An operating switch connected in series to a field and an armature, a positive characteristic heat-sensitive resistance circuit connected in parallel to the operating switch, and a brake that forms a closed circuit with the armature. What is claimed is: 1. A dynamic braking device for a series motor, characterized in that the operating switch and the braking switch can be selectively closed. (2) The dynamic braking device for a series motor as set forth in claim 1, wherein the positive characteristic heat-sensitive resistance circuit comprises a positive characteristic heat-sensitive resistance element. (3) The dynamic braking device for a series motor as set forth in claim 1, wherein the positive temperature sensitive resistance circuit comprises a series circuit of a positive temperature sensitive resistance element and a resistor. (4) A PTC heat-sensitive resistance circuit includes a plurality of PTC heat-sensitive resistance elements having different characteristics, and a plurality of resistors connected in series to each PTC heat-sensitive resistance element, and each PTC heat-sensitive resistance element and each resistor are connected in series. A dynamic braking device for a series motor according to claim 1, wherein each of the series circuits is connected in parallel to an operation switch.