Electricity: motive power systems – Plural diverse motor controls – Running-speed control
Reexamination Certificate
2002-07-02
2003-11-18
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Plural diverse motor controls
Running-speed control
C318S434000
Reexamination Certificate
active
06650075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fan motor, and more particularly to a fan motor provided with a self-diagnosis feature.
2. Description of the Prior Art
A fan motor being used in the background art includes a stator, a rotor, a Hall device, a microcomputer and a current control circuit. The stator has a stator coil mounted on it. The rotor includes a permanent magnet and a fan, and is rotatably supported to oppose the stator coil. The Hall device detects a magnetic pole position of the permanent magnet. The microcomputer processes the output of the Hall device. The current control circuit receives the output of the microcomputer and controls the operation of the rotor by controlling current to be fed to the stator coil.
Such a fan motor is installed, for example, in a casing of electronic equipment, and is an important component that discharges heat inside of the casing to assure the safe operation of the electronic equipment. Accordingly, the operating or service life of the fan motor has an important effect on the operating lives of the electronic equipment in the casing in which the fan motor is installed.
An operating life of a fan motor is estimated based on results of continuous running tests for a large number of samples. However, there is a problem that it is difficult to exactly determine a service life of an individual fan motor actually in use, based only on the results of the continuous running tests using samples, since service lives of fan motors vary according to the individual service conditions.
Further, some fan motors are provided with protection circuits. The protection circuit detects the rotational speed of the fan motor from an output voltage of the Hall device, determines that the fan motor is incurring an overload when the detected rotational speed is lower than the reference value and stops the fan motor. However, there is a problem that such a protection circuit does not work as a protection device in the abnormal case when the rotational speed of the fan motor exceeds an allowable value for some reason, and a voltage induced in the stator coil exceeds the voltage capacity of a semiconductor device in a current control circuit.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above problems and provide a fan motor provided with a self-diagnosis device or function.
It is another object of the present invention to provide a fan motor provided with a self-diagnosis device or function that determines if the fan motor has exhausted its service life.
It is still another object of the present invention to provide a fan motor provided with a self-diagnosis device or function that provides protection for control circuit devices.
One or more of these and other objects are accomplished by a fan motor comprising a stator on which a stator coil is mounted; a rotor comprising a permanent magnet and a fan and being rotatably supported to oppose said stator coil; a Hall device for detecting a magnetic pole position of said permanent magnet; current control means for controlling rotation of said rotor by controlling current to be fed to said stator coil; and self-diagnosis means for detecting the state of said fan motor, wherein an operation of said fan motor is controlled through said current control means based on a result from said self diagnosis means, wherein said self-diagnosis means includes a current detection circuit for detecting an instantaneous current value in said stator coil, current signal processing means for processing said instantaneous current value, and memory means for processing and storing a steady state current value, said instantaneous current value being compared with said steady state current value for determining if said fan motor has exceeded a service life of said fan motor if a difference between said instantaneous current value and said steady state current value exceeds a predetermined value, wherein said current signal processing means further includes zero timing generator means for receiving an output voltage from said Hall device and for generating a zero timing signal, timing signal generator means for receiving said zero timing signal and for generating a timing signal, sampling means for receiving said timing signal and for sampling said currently flowing current value, A/D converter means for transforming said sampled currently flowing current value into a digital value, and comparator means for comparing, at any time starting from receipt of said zero timing signal, said digital value of said instantaneous current value with a digital value of said steady state current value stored in said memory device, and said fan motor is determined to have exceeded the service life if the difference between said digital value of said instantaneous current value and said digital value of said steady state current value exceeds the predetermined value.
This fan motor is capable of being controlled autonomously, since the self-diagnosis device detects the state of the fan motor, based on the result of which the operation of the fan motor is controlled through the current control device.
Further to achieve the above object, the self-diagnosis device includes a current detection circuit for detecting a currently flowing current value in the stator coil, a current signal processing means for processing the currently flowing current value, and a memory means for processing and storing a steady state current value, in which the currently flowing current value is compared with the steady state current value, and the fan motor is judged to have exceeded the service life if the difference between the instantaneous current value and the steady state current value exceeds a predetermined value.
The fan motor provided with the above-described self-diagnosis device can be replaced properly when the service life of the fan motor has been exhausted, and consequently, the service lives of the electronic equipment for which the fan motor is provided can be increased, since the instantaneous current value is compared with the steady state current value, and the fan motor is judged to have exhausted its service life if the difference between the instantaneous current value and the steady state current value exceeds a predetermined value.
One or more of these and other objects are accomplished by a fan motor comprising a fan motor comprising a stator on which a stator coil is mounted; a rotor including a permanent magnet and a fan and being rotatably supported to oppose said stator coil; a Hall device for detecting a magnetic pole position of said permanent magnet; current control means for controlling rotation of said rotor by controlling current fed to said stator coil; and self-diagnosis means for detecting the state of said fan motor, wherein an operation of said fan motor is controlled through said current control means based upon a result of said self-diagnosis means, wherein said self-diagnosis means further includes reference voltage generator means for generating a predetermined reference voltage, F/V converter means for transforming a rotational speed detected by use of an output voltage of said Hall device into a voltage proportional to said rotational speed, and comparator means for comparing said reference voltage with said voltage proportional to said rotational speed, wherein said current fed to said stator coil is interrupted when said voltage proportional to said rotational speed is higher than said reference voltage, and said current fed to said stator coil is cut-off and automatically restarted to return said fan motor into normal operation when said voltage proportional to said rotational speed is less than or equal to said reference voltage.
The fan motor provided with such a self-diagnosis device can be prevented from an accident in which a semiconductor device in the current control means is destroyed, since when the rotational speed of the fan motor becomes higher than an allowable value, the current fed to the stator coil is interrupted, the rotati
Kataoka Koji
Otsuka Motoi
Birch & Stewart Kolasch & Birch, LLP
Japan Servo Co. Ltd.
Miller Patrick
Nappi Robert E.
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