Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-06-12
2001-11-06
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S603000, C318S254100, C318S132000, C318S434000, C388S809000
Reexamination Certificate
active
06313601
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the speed control of electric motors, and specifically to improvements in a speed control system for motors, particularly those suitable for use in a disk drive, such for example as a CD-ROM drive, for moving the transducer or pickup assembly across the track turns of the rotating data storage disk, among other applications.
Brushless d.c. motors have found widespread use for rotating a data storage disk or for moving a transducer across the data tracks on the disk. Fine control of motor speed is an absolute requirement in such applications. U.S. Pat. No. 5,371,635 to Sakaguchi et al., assigned to the assignee of the instant application, is hereby cited as teaching a system for generating pulses indicative of the angular position and rotational speed of a data storage disk. This prior art system is unsatisfactory for its complexity and expensiveness of construction as an inevitable result of the use of a motor speed sensor aside from the control electronics.
Japanese Unexamined Patent Publication No. 3-16066 suggests, for speed control of a brushless d.c. motor, to utilize the Hall-effect devices, the magnetoelectric converters, that have been customarily built into this type of motor for detection of the angular position of its rotor relative to the stator. The rotor position signals produced by the magnetoelectric converters are differentiated and further processed into a motor speed signal indicative of the actual rotational speed of the motor preparatory to motor speed control.
This second prior art system gains a definite advantage over the first recited one in that it does without any dedicated motor speed sensor. It is still objectionable, however, first because the control electronics, particularly those for production of the motor speed signal from the rotor position signals supplied by the magnetoelectric converters, is not as simple and inexpensive as can be desired. Secondly, the motor speed signal so produced is inconveniently high in ripple percentage, running counter to the objective of fine motor speed control.
SUMMARY OF THE INVENTION
The present invention has it as an object, in producing the motor speed signal without use of a motor speed sensor as above, to minimize the ripple of the motor speed signal for controlling the motor speed with a minimum of errors.
Another object of the invention is, in speed control of a brushless d.c. motor without use of a motor speed sensor of any kind, to materially simplify the circuitry for production, from the rotor position signals supplied by the standard magnetoelectric converts, of a motor speed signal which indicates the actual rotational speed of the motor and which is needed for its speed control.
Briefly, the present invention may be summarized as a speed control system for a motor of the type having magnetoelectric converter means for providing a first, a second and a third rotor position signal with phase differences of 120 degrees therebetween, each rotor position signal being indicative of the angular position of a rotor relative to a stator. The motor speed control system comprises differentiating circuit means for differentiating the first, the second and the third rotor position signal and providing a first, a second and a third output signal in a prescribed phase relationship with the first, the second and the third rotor position signal, respectively. A first, a second and a third switch are provided for selectively passing the first, the second and the third output from the differentiating circuit means under the control of a first, a second and a third binary switch control signal, respectively. The first, the second and the third switch control signals are derived from the first, the second and the third rotor position signal in a prescribed phase relationship therewith. Outputs from the three switches are added together into a motor speed signal representative of the actual rotational speed of the motor. The motor speed signal is compared with a target speed signal representative of a desired rotational speed of the motor, thereby providing a motor speed control signal indicative of the difference between the actual and the desired motor speeds. A motor excitation circuit responds both to the first, the second and the third rotor position signal and to the speed control signal for causing the motor to rotate at the desired speed.
The invention is applicable to brushless d.c. motors, d.c. motors with brushes, and alternating current motors. The motor speed signal is obtained from the rotor position signals supplied from the Hall-effect devices or like magnetoelectric converters. For production of the motor speed signal from the rotor position signals, these signals must be differentiated, and parts of the resulting signals must be extracted, or the resulting signals put to what is essentially equivalent to half- or full-wave rectification, prior to being added together into the motor speed signal.
Such extraction or rectification is accomplished according to the invention as the first to third switches selectively pass the first to third outputs from the differentiating circuits under the control of the first to third binary switch control signals. The present invention particularly features the creation of the switch control signals by shaping the rotor position signals, which are in the form of sine waves, into binary signals. With the motor speed signal produced in this manner, the complete speed control system is greatly simplified in construction compared to the closest prior art set forth above.
According to another feature of the invention, the rotor position signals are 30 degrees delayed in phase before being turned into binary signals for switch control. Desired segments of the rotor position signals can be ideally extracted by controlling the switches by these binary switch control signals, resulting in the provision of a motor speed signal, or speed control signal, that is less in ripple percentage.
A further embodiment is disclosed which employs an operational amplifier in place of a simple adder for combining the outputs from the switches. The operational amplifier performs the dual function of differentiation and addition of the outputs from the switches, or even the multiple function of the differentiation and addition of the switch outputs and the comparison of the resulting motor speed signal with the target speed signal, thereby contributing to greater simplicity in circuit arrangement.
There is also disclosed herein a yet further embodiment that employs another set of switches which coact with the first recited set of switches for what is equivalent to full-wave rectification of the outputs from the differentiating circuit means. The resulting motor speed signal, or speed control signal, is still more reduced in ripple percentage.
The above and other objects, features and advantages of this invention and the manner of achieving them will become more apparent, and the invention itself will best be understood, from a study of the following description and attached claims, with reference had to the accompanying drawings showing the preferred embodiments of the invention.
REFERENCES:
patent: 5371635 (1994-12-01), Sakaguchi et al.
patent: 5471451 (1995-11-01), Masaki et al.
patent: 5717537 (1998-02-01), Watanabe et al.
patent: 03016066-A (1991-01-01), None
Kubo Mitsumasa
Tanaka Masashi
Masih Karen
Teac Corporation
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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