JPS5854756B2 - Generating brake device for AC series-wound commutator motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dynamic braking device for an AC series-wound commutator motor.

For electric motors for power tools such as circular saws, switch O
There is a legal requirement that the brake must stop within 10 seconds after the switch is turned off, and when the switch is turned off, the brake system generally uses an electric motor as a generator to convert the rotational energy of the armature into electrical energy. , a dynamic brake that performs a braking action using the armature reverse rotation force at that time is often used.

There are two types of dynamic brakes: a separate excitation type in which the field is generated by a separate power source, and a self-excitation type in which the residual magnetism is utilized when the switch is turned off.

When the above self-exciting type dynamic brake device is used in an AC commutator motor, the dynamic brake may not function even if the switch is turned off.

That is, since the current is alternating current and draws a sinusoidal waveform as shown in Figure 1a, the residual magnetism changes as the current changes, drawing a hysteresis curve, and the braking force of the dynamic braking action also changes depending on the residual magnetism. In the phase range t1, which is centered around zero of the sinusoidal waveform of the current, the residual magnetism cannot contribute to the braking action or is zero. Even if the switch is turned OFF and the power is cut off at t1, the motor does not function sufficiently as a generator, and the braking force becomes too small or zero, and i
It cannot fulfill its role as a power generating brake.

In particular, even in the case of a multi-phase series-wound commutator motor, currents of the same phase flow through each field winding, so if the residual magnetism in the negative field winding is small, the residual magnetism in the other field windings will increase. Similarly, there are few (,
Dynamic braking action could not be performed.

As mentioned above, the self-excited dynamic braking device used in AC series-wound commutator motors has the disadvantage that the brake does not work once every few times, and although it is extremely dangerous, The reality is that they are sold as they are because they are so rare.

In addition, in the above-mentioned dynamic braking device, the switch is turned OFF and the power is turned off outside the phase range t1 in which the residual magnetism cannot contribute to the braking action, that is, within the phase range t2 where the residual magnetism can contribute to the braking action. If the switch is shut off, a sufficient braking action can be achieved, but the magnitude of the spark generated at the switch changes depending on the magnitude of the current when the switch is OFF, as shown by the line in Figure 1. Turning off the switch near the maximum value of the current just because the force is large is
The sparks generated at the switch will also be large, resulting in early burnout of the switch, weakening of its durability, and shortening its lifespan.

Therefore, when turning off the switch and cutting off the power,
Within the phase range t2 in which the residual magnetism can contribute to the braking action, it is most appropriate that the spark is small, that is, near the phase range t1 in which the residual magnetism cannot contribute to the braking action. did not give any consideration to this point.

The present invention solves the above-mentioned drawbacks of the conventional technology, and enables dynamic braking to be applied at all times no matter when the switch is turned off, and the spark generated at the switch is small, extending the life of the switch. The phase detecting means detects the phase of the motor's operating current, and when the switch is OFF, the phase detecting means communicates with the residual magnetism in the phase range t2 in which the residual magnetism can contribute to the braking action. The brake circuit forming means is activated near the phase range t1 in which the brake cannot contribute to the braking action, and the power source is cut off to form the brake circuit.

Next, embodiments of the present invention will be described with reference to the drawings.

The circuit diagram in Figure 2 shows an embodiment of the present invention in the basic type of an AC series-wound commutator motor.
To explain using the block diagram shown in the figure, 1 is an armature winding of a motor, 2 is a field winding, and 3 is a power source.

Reference numeral 4 denotes a phase detection means provided to detect the phase of the operating current of the motor, and this phase detection means 4 may be constructed using a well-known phase detection circuit or the like.

5 is a brake circuit forming means, and the phase detecting means 4
The phase detection means 4 and the brake circuit formation means 5 are connected so that the detected phase can be communicated to the brake circuit formation means 5.

Then, when the switch (not shown in FIG. 2) is turned off, the brake circuit forming means 5 receives the communication from the phase detecting means 4 and determines that the current value is within the phase range t2 in which the residual magnetism can contribute to the braking action. The brake circuit is formed by cutting off the power supply 3 at a predetermined time point P near the phase range t1 when the residual magnetism is as small as possible, that is, when the residual magnetism cannot contribute to the braking action.

The predetermined time point P may be determined by experiment, and for example, as shown in FIG.
, 180°−α.

All or some of the time points of 180°+α and 3600−α are set as the above-mentioned time point P.

The brake circuit forming means 5 may be constituted by a well-known control circuit, a changeover switch, and other electronic components.

In the present invention having such a configuration, the phase of the operating current of the electric motor is detected by the phase detection means and communicated to the brake circuit forming means.

Then, when the switch is turned off to stop the electric motor, the brake circuit forming means receives communication from the phase detection means and determines that if the phase when the switch is turned off is within the phase range t1 in which residual magnetism does not contribute to the braking action. Of course, the phase range t in which the residual magnetism can contribute to the braking action is
2, if the phase is other than the predetermined time P near the phase range t1, the current is passed for a moment without turning off the power at the same time, and the phase is at the predetermined time P. When the phase is 1-, the power is cut off and a brake circuit is formed.

Furthermore, the time during which the current continues to flow when the switch is OFF is as follows:
Since several predetermined time points P are set in one cycle, the time is extremely short.

Of course, if the switch-off time is the predetermined time P, the power is cut off at the same time, and a brake circuit is formed.

As described above, the present invention detects the phase of the operating current of the motor using the phase detection means, and when the switch is OFF, the residual magnetism is close to the phase range in which the residual magnetism cannot contribute to the braking action, especially within the phase range in which the residual magnetism can contribute to the braking action. The brake circuit forming means is activated by selecting a predetermined point in time, and the power is cut off at this predetermined point to form the brake circuit. The residual magnetism when the power is cut off can sufficiently contribute to the operation of the motor as a generator, and the dynamic braking action can be performed reliably, and the brake can always be applied completely, resulting in a high level of safety.

Moreover, since the point in time when the power is actually cut off and the brake circuit is formed is set close to the phase range in which residual magnetism cannot contribute to braking action, the current value is small even within the phase range in which residual magnetism can contribute to braking action. The sparks generated in the switch part when the switch is turned off are small, preventing burnout caused by sparks, deterioration of durability, etc., and significantly extending the life of the switch compared to conventional ones.

As described above, the present invention can cut off the power supply and form the brake circuit when the switch is turned off at the most appropriate time from the viewpoint of braking action and spark generation, and can be used as a conventional dynamic braking device for an AC series-wound commutator motor. This is an invention that has excellent effects.

[Brief explanation of drawings]

Fig. 1a is a waveform diagram of alternating current, the same figure is a curve diagram showing the braking force and spark generation state with respect to the current, Fig. 2 is a circuit diagram showing an embodiment of the present invention in a basic type of electric motor, and Fig. 3 is a block diagram of the device of the present invention. DESCRIPTION OF SYMBOLS 1... Armature winding of electric motor, 2... Field winding, 3... Power supply, 4... Phase detection means, 5... ...brake circuit forming means, tl...
...Phase range in which residual magnetism cannot contribute to braking action, t2... Phase range in which residual magnetism can contribute to braking action, P... Time point at which the brake circuit forming means is activated.

Claims (1)

[Claims] 1. In a dynamic braking device for an AC series-wound commutator motor that performs dynamic braking using residual magnetism generated in a field winding, a means for detecting the phase of the operating current of the motor and a switch OFF are used.
and a means for forming a brake circuit by cutting off the power supply at a predetermined time point near a phase range in which the residual magnetism cannot contribute to braking action within a phase range in which residual magnetism can contribute to braking action in response to communication from the phase detection means. A dynamic braking device for an AC series-wound commutator motor.