JPH1023656A - Overload protection device for dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overload protection device, having high reliability for a DC motor equipped with an encoder. SOLUTION: Thermistors 27 and 30 are arranged on an encoder substrate 23 and in a DC motor, and the temperature is detected from both of them. Then, the DC motor is stopped by a chopper controller when the temperature reaches a certain value for protecting the DC motor, even though the time to reach a limit temperature of armature winding of a DC motor and the time to reach the limit temperature of the encoder do not conform to a certain rule, because of the difference in the load of a DC motor 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor overload protection device.

[0002]

2. Description of the Related Art In recent years, it has become mainstream to employ a device for effectively controlling the rotation speed of a DC motor using a chopper control device in a DC motor equipped with an encoder.

Hereinafter, a conventional DC motor overload protection device will be described with reference to FIGS. 2 and 3. FIG.

FIG. 2 is a partial sectional view of a conventional DC motor.
Encoder board 3 via bracket 2 with bracket 1
Is installed. A code wheel 5 for controlling transmission and blocking of light of a photo interrupter 4 mounted on an encoder board is mounted on the rotating shaft 6.

FIG. 3 is a block diagram for explaining the operation of the overload protection device. The chopper control device 7 is provided with a thermistor 9 as a temperature sensing element for detecting heat generation of a power circuit on its printed circuit board.

The operation of the overload protection device for a DC motor configured as described above will be described below.

First, when the DC motor 8 is operated, the rotating shaft 6
The code wheel 5 attached to the photo-interrupter 4 rotates, and the optical signal of the photo-interrupter 4 is transmitted and blocked, and an output signal synchronized with the rotation speed is generated. Upon receiving this output signal, the chopper control device 7 controls the rotation speed of the DC motor 8. The current flowing through the power circuit of the chopper control device 7 increases or decreases depending on the magnitude of the load of the DC motor 8, and the temperature of the printed circuit board of the chopper control device 7 changes. When the temperature detected by the thermistor 9 mounted on the substrate reaches the set temperature of the thermistor 9 which is correlated with the use limit temperature of the armature winding of the DC motor 8, the signal to the power circuit is stopped and the DC motor is stopped. 8 is stopped to provide overload protection.

[0008]

However, in the above conventional configuration, the temperature of the printed circuit board of the chopper control device 7 is detected to indirectly estimate the temperature of the armature winding of the DC motor. The temperature of the armature winding of the DC motor and the temperature of the encoder section are not correctly determined due to the difference in the load condition of the DC motor, and the DC motor may be burned, the encoder may be heated and damaged, or the DC motor may be stopped. However, it has a problem that it is too early to exhibit a sufficient function.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a highly reliable overload protection device for a DC motor equipped with an encoder.

[0010]

According to the present invention, there is provided a DC motor equipped with an encoder having a structure in which a temperature sensing element is disposed inside an encoder substrate and the DC motor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a DC motor equipped with an encoder for detecting a rotational speed, which is an overload protection device for a DC motor in which a temperature sensing element is arranged on an encoder substrate and inside the DC motor. Yes, a thermistor is placed on the encoder board and inside the DC motor to detect both temperatures, so the DC motor can be stopped by the chopper control device when the DC motor reaches the operating limit temperature. is there.

[0012]

An embodiment of the present invention will be described below with reference to FIG.

(Embodiment 1) FIG. 1 is a partial sectional view of an overload protection device according to an embodiment of the present invention. An encoder board 23 is mounted outside a bracket 21 of a DC motor 32 via a spacer 22. A photo interrupter 24 is mounted on the encoder board 23, and the DC motor 3
The transmission and blocking of light of the photointerrupter 24 are controlled by the code wheel 25 mounted on the second rotating shaft 26. A thermistor 27 which is a temperature-sensitive element for detecting the ambient temperature is mounted on the encoder board 23. A thermistor 30 is mounted on the brush holding substrate 29 near the brush 28 in order to detect the temperature inside the DC motor.

The operation of the overload protection device configured as described above will be described. First, when the DC motor 32 is operated, the code wheel 2 attached to the rotating shaft 26 is rotated.
By rotation of 5, the optical signal of the photo interrupter 24 is transmitted and blocked, and an output signal synchronized with the rotation speed is generated. Upon receiving the output signal, the chopper control device controls the rotation speed of the DC motor 32.
The above is the same as the conventional operation. And the DC motor 3
The temperature inside the DC motor or the temperature of the encoder changes depending on the magnitude of the load 2 and is detected by the thermistor 27 mounted on the encoder substrate 23 and the thermistor 30 mounted on the brush holding substrate 29 near the brush 28. Depending on the temperature, the chopper control device stops the DC motor 32 when one of them reaches a set value, thereby providing overload protection.

As described above, since the thermistor is disposed inside the encoder board and the DC motor to detect both temperatures, the time required for the temperature of the armature winding of the DC motor to reach the limit value due to the difference in the load of the DC motor. Even if the time when the temperature of the encoder reaches the limit temperature does not follow a certain rule, the DC motor can be stopped by the chopper control device when the temperature of the DC motor has to be protected.

Although the position of the thermistor 30 in the DC motor is set on the brush holding substrate 29, another position may be used as long as the temperature near the armature winding, the commutator and the brush 28 can be accurately detected. .

[0017]

As described above, according to the present invention, since the thermistor is disposed inside the encoder substrate and the DC motor to detect both temperatures, the DC motor can be burned under any load. Alternatively, the encoder can be prevented from being damaged, and a highly reliable overload protection device for a DC motor can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of an overload protection device according to an embodiment of the present invention.

FIG. 2 is a partial sectional view of a conventional DC motor.

FIG. 3 is a block diagram illustrating the operation of a conventional overload protection device.

[Explanation of symbols]

 21 Bracket 23 Encoder board 27, 30 Thermistor 32 DC motor

Claims (1)

[Claims] An overload protection device for a DC motor provided with a temperature-sensitive element on an encoder substrate and inside the DC motor in a DC motor equipped with an encoder for detecting a rotation speed.