Electricity: motive power systems – Limitation of motor load – current – torque or force
Patent
1995-07-16
1998-10-20
Masih, Karen
Electricity: motive power systems
Limitation of motor load, current, torque or force
318445, 361 1, H02K 1732
Patent
active
058251448
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a highly safe drive control apparatus for a rotating machine, which controls the supply of current to a motor while monitoring rotation of a movable part rotatably driven by the motor.
BACKGROUND ART
For example, with a reaction apparatus used in a chemical factory for stirring and mixing materials such as solids to produce a reaction, a stirring rod is provided inside a large mixing vessel, which is rotatably driven by a motor to thereby stir and mix the materials inside the vessel. In this case, if rotation of the stirring rod stops during stirring, due for example to failure of the motor shaft or a gear section which mechanically connects the motor to the stirring rod, so that stirring ceases, then normal mixing is no longer possible even though the reaction apparatus is operating. Local chemical reaction of the materials can thus occur causing high temperatures. If this situation continues for too long, there is the likelihood of a serious accident with damage to the reaction apparatus.
To prevent such an accident, it is necessary in the safe drive control of a rotating machine incorporating a rotatably movable part rotated by a motor, to indicate as a danger condition a state where rotation of the movable part has stopped even though a current is flowing in the motor. Accordingly, with this drive control system, it is necessary to have a construction such that a signal indicating safety is produced when the movable part is rotating, with the motor current being supplied based on the safety indicating signal, and such that a signal indicating danger is produced when the movable part is not rotating even though a current is being supplied to the motor, with the motor current supply being stopped based on the danger indicating signal.
However, with such a system structure, a contradiction arises at the time of start up of the rotating machine since at this time, because the movable part is not rotating, the signal indicating danger will be produced, so that current will not be supplied to the motor and hence the motor can not be driven.
Moreover, in general a warning device is provided for warning of a danger condition which is created when the movable part is stopped when it should be rotating.
When in this case a lamp is used for the warning device, then if the construction is such that at the time of a safe condition (the movable part is rotating when it should be rotating) a green lamp comes on, while at the time of a danger condition (the movable part is stopped when it should be rotating), the lamp is extinguished, then a fail-safe construction results wherein for example, when a lamp burn out fault occurs, the extinguishing of the lamp indicates danger.
However, when a speaker or buzzer and the like is used as a warning device, then with the construction (ie. fail-safe construction) as with the abovementioned lamp, wherein an output is produced at the time of safety, while at the time of danger, the output is extinguished, since the situation will normally be safe, a sound will be continuously produced from the speaker or buzzer resulting in a disturbing noise. Therefore warnings from a speaker or buzzer are normally used with a method wherein a sound is only produced at the time of danger, that is to say a drive output for the speaker or buzzer is only produced at the time of a danger condition. However, with such a normal use method, since sound producing energy is not produced under normal situations, then there is a problem when the situation arises wherein a real danger needs to be reported but cannot due to a fault.
The present invention takes into consideration the above situation, with the object of solving, with a fail-safe construction, the contradiction in the system wherein motor drive permission is granted after verifying the rotation stop condition of a movable part, that at the time of start-up the motor cannot be driven due to the movable part being stationary. Moreover, it is a further object of the present invention, in the cas
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patent: 4235085 (1980-11-01), Torita
patent: 4661880 (1987-04-01), Futsuhara
patent: 4675935 (1987-06-01), Kasper et al.
patent: 4757417 (1988-07-01), Futsuhara
patent: 5027114 (1991-06-01), Kawashima et al.
patent: 5218541 (1993-06-01), Sakakibara et al.
Futsuhara Koichi
Sakai Masayoshi
Suzuki Masatoshi
Kao Corporation
Masih Karen
The Nippon Signal Co. Ltd.
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