Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1990-09-04
1992-11-17
Paschall, Mark H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219494, 219490, H05B 102
Patent
active
051645726
DESCRIPTION:
BRIEF SUMMARY
Background of the Invention
This invention relates to an abnormal temperature detection device for a regeneration resistor which processes the regenerative energy of an electric motor or the like by heat generation. More particularly, the present invention relates to an abnormal temperature detection device for a regeneration resistor in a small-sized spindle motor, servomotor or the like used in an NC machine tool or industrial robot.
A regeneration resistor is mounted on a small-sized spindle motor, servomotor or the like used in an NC machine tool or industrial robot, to consume a regenerative energy thereof.
To detect an abnormal temperature of the regeneration resistor, the regeneration resistor is covered with cement and set into a metal case, to thereby increase the surface area of the regeneration resistor so as to suppress a rise in the temperature thereof. A thermostat is mounted on the surface of the metal case, whereby when an abnormal increase of the temperature of the regeneration resistor occurs, the abnormal temperature is detected and countermeasure is taken by, for example, turning off the power source of the numerical control device.
When the operation of a cooling fan for forcibly air-cooling the regeneration resistor is interrupted, or a transistor of a control circuit for controlling the current in the regeneration resistor becomes defective, the temperature of the regeneration resistor becomes higher. Therefore, a correct detection of an abnormal temperature rise must be realized.
Nevertheless, since the regeneration resistor is formed by only a resister, a metal case, and an insulation member for isolating these members from each other, the surface temperature of the regeneration resistor is as high as several hundred .degree. C. even during a normal operation. Therefore, if a thermostat which is generally used at such high temperatures is set in direct contact with the regeneration resistor, the solder therein may melt or the metal portion max oxidize.
Further, the regeneration resistor is forcibly aircooled by a cooling fan to suppress any rise in the temperature of the regeneration resister. Therefore, a defect in the insulation in the thermostat may be easily caused by dust in the duct, making it difficult to correctly detect the temperature of the regeneration resistor.
Summary of the Invention
An object of the present invention is to provide an abnormal temperature detection device for a regeneration resistor in which a thermostat able to detect temperatures of approximately 100.degree. C. is used to detect temperatures higher than approximately 100.degree. C.
To solve the above-described prior art problems, the present invention provides an abnormal temperature detection device for a regeneration resistor for consuming the regenerative energy of an electric motor. The abnormal detection device comprises a heat conductive member mounted in contact with the surface of the regeneration resistor and a thermostat for detecting a temperature rise due to an abnormal heat generation in the regeneration resistor, via the heat conductive member. The thermostat and the regeneration resistor are provided in different spaces.
The surface temperature of the regeneration resistor, which is set high, is not directly detected. The thermostat is mounted on a portion at which the temperature is lowered via the heat conductive member and the temperature of the portion is detected. As a result, 100.degree. C. can be used to detect temperatures higher than approximately 100.degree. C., thereby making it possible to detect an abnormal heat generated in the regeneration resistor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) to 1(c) are diagrams of an embodiment of the present invention; and
FIG. 2 is a graph of a heat radiation characteristic obtained when a regeneration resistor having a resistance of 16.OMEGA. is used in the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of this invention will be described with reference to the accompanying drawings.
FIGS. 1(a) to 1(c)
Fanuc Ltd.
Paschall Mark H.
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