Electricity: motive power systems – Open-loop stepping motor control systems
Patent
1998-08-04
2000-02-22
Nappi, Robert E.
Electricity: motive power systems
Open-loop stepping motor control systems
327164, H02P 800
Patent
active
060284129
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and apparatus for generating a clock signal. In this application, the term "clock signal" is defined as a series of periodic signals which may be used to clock any particular electronic circuit or device at a fixed or variable frequency. In particular, the clock signal may be used in the generation of any waveform, potentially replacing RC and RL circuits, bistables, sweeping frequency generators, error correcting amplifiers and phase locked loops.
BACKGROUND ART
The generation of a known frequency is common in many commercial applications, including radio equipment, mobile phones, two way radios, television and radio frequency tuners. The need for digital control in such tuners has brought about dedicated phase locked loop integrated circuits which are expensive. These circuits have limitations as they have a predetermined discrete number of frequencies and pre-determined range of frequencies which they can generate. Such an arrangement is commonly seen when tuning a digital car radio where the FM frequency changes in steps of typically 0.1 MHz over a 20 MHz range.
Frequency control is also used in motor controllers, particularly in stepper and DC motor applications where a clock signal controls the speed of the motor. Varying the frequency of the clock signal controls the speed of the rotor. There are many established methods of translating the frequency of a clock signal to drive many different types of electrical motors and many commercially available integrated circuits which perform such translation. Conventional stepper controllers can typically only produce around 250 different predetermined stepping rates so that when the stepping rate needs to be changed it can only be done in a stepwise fashion. Accordingly, it is impossible to obtain a smooth change from one stepping rate to another, which is highly desirable in some applications.
DISCLOSURE OF INVENTION
According to a first aspect of the present invention, a method of generating a clock signal having a desired frequency comprises the step of generating a pulse each time a stored accumulator value is found to be greater than or equal to a stored trigger value, wherein in a first loop the stored accumulator value is iteratively incremented by a first iterative value until the stored accumulator value is greater than or equal to the stored trigger value and subsequently in a second loop the stored accumulator value is decremented by a second iterative value until the stored accumulator value is less than the stored trigger value and, wherein signal is compared to a desired frequency value and if the two values are different, the first iterative value is corrected at a predetermined rate over one or more subsequent iterations until the frequency of the generated clock signal corresponds to the detected value of the desired frequency.
Preferably, under conditions where the generated clock signal frequency equals the desired frequency, the first iterative value is set by the value of a detected input corresponding to the desired frequency of the clock signal. An iterative increment equal to the detected value of the desired frequency in Hertz is added to the stored accumulator value during each iteration of the first iterative loop. When the desired frequency of the clock signal changes, the first iterative value is corrected at a predetermined rate over one or more subsequent iterations until the frequency of the generated clock signal, and consequently the first iterative value, corresponds to the detected value of the desired frequency. Accordingly, the frequency of the clock signal is capable of accelerating between two frequencies at a predetermined rate without missing any intermediate frequencies. In the context of a stepper motor, this means that the stepping rate can be accelerated in a manner which approximates very closely to a continuous function.
Preferably, the second iterative value is set by the stored trigger value, whereby the stored trigger value is at least that in
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Shine Ian Basil
Shine Thomas Adam
Duda Rina I.
Nappi Robert E.
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