Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-09-12
2001-11-20
Donels, Jeffrey (Department: 2816)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S139000, C318S798000, C318S434000, C318S714000, C388S909000
Reexamination Certificate
active
06320339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control device for controlling current passing through a motor, more particularly to a control device for minimizing the presence of ripples in the current passing through the motor.
2. Description of the Related Art
A conventional control device for controlling current passing through a motor includes a pulse width modulator, a power module, and a current limiter for limiting the current passing through the motor. The current limiter includes a current detector provided to detect the current passing through the motor. When the detected current exceeds a predetermined value, an inhibit signal is produced by the current limiter and is sent to the power module to stop the supply of power to the motor. When the detected current drops below the predetermined value, the current limiter dismisses the inhibit signal to the power module to once again permit the supply of power to the motor. However, the inhibit signal is associated with a hysteresis action, and is not synchronous with the pulse width modulated control pulses generated by the pulse width modulator. Therefore, due to the different performance characteristics of the motor, the inhibit signal cannot be reset in each of the pulse width modulated cycles, thereby resulting in a relatively large ripple current to the motor.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a control device for controlling stability of current passing through a motor so as to minimize the presence of ripples.
According to the present invention, a control device is adapted for controlling current passing through a motor. The control device includes a power module, a current sensor, a first current detecting circuit, a second current detecting circuit, and a processor.
The power module is adapted to be connected to the motor and a power supply unit.
The current sensor is connected to the power module and generates an electric signal corresponding to magnitude of the current passing through the motor.
The first current detecting circuit is connected to the current sensor and the power module. The first current detecting circuit determines whether the current passing through the motor is larger than a first predetermined value according to the electric signal from the current sensor, and generates a first flag signal that is provided to the power module so as to inhibit connection between the motor and the power supply unit upon detection that the current passing through the motor is larger than the first predetermined value.
The second current detecting circuit is connected to the current sensor and the power module. The second current detecting circuit determines whether the current passing through the motor is larger than a second predetermined value according to the electric signal from the current sensor, and generates a second flag signal that is provided to the power module so as to inhibit connection between the motor and the power supply unit upon detection that the current passing through the motor is larger than the second predetermined value. The second predetermined value is larger than the first predetermined value.
The processor is connected to the first and second current detecting circuits. The processor generates a first flag reset signal to the first current detecting circuit at a first reset frequency for resetting the first flag signal periodically. The processor further generates a second flag reset signal to the second current detecting circuit at a second reset frequency for resetting the second flag signal periodically. The first reset frequency is larger than the second reset frequency.
As such, connection between the motor and the power supply unit is inhibited for a period of time that is longer when the second flag signal is provided to the power module than when the first flag signal is provided to the power module.
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Chiu Sheng-Lin
Lin Rick
Donels Jeffrey
Duda Rina I.
Ladas & Parry
Universal Scientific Industrial Co., Ltd.
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