Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
1999-12-29
2001-07-24
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S254100, C388S804000
Reexamination Certificate
active
06265841
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for driving a multi-phase d.c. motor, the device including a multi-phase inverter for applying drive signals to the windings of the motor in such a manner that said windings are recurrently driven in a given sequence by the drive signals, the drive signals being pulse-width modulation to control the speed of the motor.
DESCRIPTION OF THE RELATED ART
A device of the type defined in the opening paragraph is known from, inter alia, European Patent Application 0419303, corresponding to U.S. Pat. No. 5,193,146.
In the known device the amount of power applied to the motor is controlled with the aid of pulse-width modulation. To raise the speed of the motor the amount of power applied to the motor is increased by increasing the pulse-width of the pulse-width modulation. To reduce the speed of the motor, the amount of power applied to the motor is reduced via the pulse-width, as a result of which the speed of the motor decreases due to the internal friction of the motor.
A drawback of the known device is that reducing the speed of the motor proceeds comparatively slowly, i.e., far more slowly than raising the speed of the motor. Thus, in the case of the known device, the motor is not slowed down or braked actively. If the motor speed is temporarily too high, it is necessary to wait until the motor has lost enough speed as a result of friction before operation at a desired speed can be resumed. This slows down the speed control. This is particularly undesirable in the case of CD-ROM drives.
To solve this problem it has been proposed to brake the motor actively by temporarily reversing the direction of flow of the drive signals applied to the motor windings. A drawback of this solution is that it is not possible to obtain a smooth transition from normal operation to active braking. If speed control is used, it is necessary that for such a transition, the current is first reduced to zero, the commutation position is adapted, and the current is raised again. This is rather difficult.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a solution to the problems outlined hereinbefore. To this end, the device in accordance with the invention is characterized in that a first and a second drive signal at a time, are applied to at least one winding of the motor, the first and the second drive signals flowing in opposite directions in the at least one winding, and the device further including pulse-width modulation means for applying a first pulse-width modulation to the first drive signal, and for applying a second pulse-width modulation to the second drive signal, the pulse-width modulation means being adapted to vary the pulse-width of the first-pulse-width modulation with respect to the pulse-width of the second pulse-width modulation, for accelerating, actively decelerating or maintaining the speed of the motor, and, if desired, for selecting a direction of rotation of the motor.
Since the pulse-width of the first pulse-width modulation and that of the second pulse-width modulation can be controlled independently of one another, it is possible to achieve a smooth transition between active speeding-up and active slowing-down (braking) of the motor. Thus, the device in accordance with the invention is capable of actively slowing down, a gradual transition being possible between active slowing-down, stabilization and speeding up of the motor. In fact, there is no longer any difference between active slowing-down and driving. Moreover, the motor in accordance with the invention can be driven in two directions and in each direction of driving, the motor speed can be raised, actively slowed down and maintained constant, as desired.
Particularly, the first duty cycle is selected to be equal to the second duty cycle for stopping the motor.
A further embodiment of the device in accordance with the invention is characterized in that the multi-phase inverter includes at least a first and a second controllable switching element for connecting a first terminal of the first winding, respectively, to a first and a second terminal of a d.c. power supply, and at least a second and a third controllable switching element for connecting a first terminal of the second winding, respectively, to the first and the second terminal of the d.c. power supply, a second terminal of the first winding being electrically connected to a second terminal of the second winding and the pulse-width modulation means generating a first control signal for switching the first switching element, a second control signal for switching the second switching element, a third control signal for switching the third switching elements and a fourth control signal for switching the fourth switching element, the first and the second control signals being pulse-width modulated in such a manner that the first and the second switching elements are not closed concurrently, the third and the fourth control signals being pulse-width modulated in such a manner that the third and the fourth switching elements are not closed concurrently, and the first and the fourth control signals each being pulse-width modulated with a first duty cycle, and the second and the third control signals each being pulse-width modulated with a second duty cycle, the first and the second duty cycles being varied with respect to one another for accelerating, actively decelerating or maintaining the speed of the motor. The advantage of this further embodiment is that the switching circuit, formed by said switching elements, is a switching circuit which is known per se and is frequently used with success. Thus, use can be made of a switching circuit which is known per se and which, in accordance with the invention, can be driven with said control signals in order to drive the motor, enabling the motor speed to be alternatively raised, actively slowed down and maintained constant with a gradual transition.
Preferably, the first and the fourth control signals are equal to one another and in that the second and the third control signals are identical and equal to one another. In accordance with this variant only two mutually different control signals have to be generated.
REFERENCES:
patent: 4528486 (1985-07-01), Flaig et al.
patent: 4928043 (1990-05-01), Plunkett
patent: 5193146 (1993-03-01), Kohno
patent: 5274317 (1993-12-01), Utley et al.
patent: 5291106 (1994-03-01), Murty et al.
patent: 5495160 (1996-02-01), Pond
patent: 5640073 (1997-06-01), Ikeda et al.
patent: 5859512 (1999-01-01), Buthker
patent: 0419303A1 (1991-03-01), None
Duda Rina I.
Goodman Edward W.
Nappi Robert E.
U.S. Philips Corporation
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