Static information storage and retrieval – Systems using particular element – Magnetostrictive or piezoelectric
Reexamination Certificate
2000-04-24
2001-12-04
Roskoski, Bernard (Department: 2859)
Static information storage and retrieval
Systems using particular element
Magnetostrictive or piezoelectric
C360S125330, C360S250000, C318S696000
Reexamination Certificate
active
06327177
ABSTRACT:
The present invention concerns a method for controlling a stepping motor including a rotor provided with a permanent magnet and a coil magnetically coupled to said magnet, said method including the application of a driving pulse to said coil each time that said rotor has to rotate by one step, said driving pulse including connection periods during which said coil is connected to an electric power source and disconnection periods during which said coil is disconnected from said source, the ratio between the total duration of said connection periods and the total duration of said disconnection periods being equal to a desired chopping rate.
The present invention also concerns a device for implementing this method.
A device and method of this type are described, for example, in U.S. Pat. No. 4,361,410 where they are illustrated in FIGS. 8 to 11. In this document, after each driving pulse a circuit generates a detection signal having a first or a second state according to whether the mechanical load driven by the rotor of the motor during such driving pulse was relatively low and the rotor has thus rotated properly, or whether said mechanical load was so high that the rotor has not rotated. A combinatorial logic circuit generates control pulses having a chopping rate of 50% or 75% according to whether the detection signal has its first or second state, and the control pulses are used to chop, with the same rate, the following driving pulse. The quantity of electric power supplied to the coil of the stepping motor is thus enslaved to the mechanical load driven by the rotor of said motor, which reduces the quantity of electric energy.
It will be recalled that a chopped driving pulse includes a certain number of periods during which the motor coil is connected to an electric power source, these connection periods being separated from each other by disconnection periods, i.e. during which the motor coil is disconnected from the power source.
It will also be recalled that the chopping rate of such a driving pulse is generally defined as being the ratio between the total duration of the connection periods which have just been mentioned and the total duration of the driving pulse. It is this definition which will be used in the following description.
It will also be noted that, in aforementioned U.S. Pat. No. 4,361,410, the definition of the chopping rate of the driving pulses is the reverse of this generally accepted definition. It follows that the rate of 0% and 25% mentioned in such document are in fact, according to the generally accepted definition, rates of 100% and 75% respectively.
Those skilled in the art will easily see that the slaving achieved by the circuit of FIG. 8 of U.S. Pat. No. 4,361,410 succinctly described hereinbefore is very scanty, and that the reduction in the electric energy consumed by the motor resulting from this control is thus very low, due to the fact that only two driving pulse chopping rates are provided.
It is of course possible to increase the number of chopping rates available, in order to improve the slaving of the quantity of electric energy provided to the motor coil to the mechanical load driven by the rotor thereof, and to further reduce the total quantity of the electric energy consumed by the motor.
However the complexity of the combinatorial logic which generates the control pulses used to chop the driving pulses increases rapidly with this number of available chopping rates. The same is of course true of the place occupied by the logic in the integrated circuit in which it is made, and consequently the cost price of the latter. It has been observed that, in practice, it is not possible to provide more that eight or ten distinct chopping rates if one wishes the cost price to remain within bearable limits. It is often desirable to have a higher number of chopping rates available in order to be able to reduce the power consumption of the stepping motor by slaving as closely as possible the quantity of electric energy provided thereto during each driving pulse to the mechanical load effectively driven by its rotor. This is particularly the case when the motor is that which drives the hands of a timepiece whose source of electric power is formed by a battery or an accumulator of small volume and thus of quite limited capacity.
It is also desirable to have available a quite high number of chopping rates when the supply voltage of the motor can vary quite significantly, as is the case when the motor is that which drives the hands of an electronic timepiece but where the power source of the latter is formed by a rechargeable system, for example by solar cells or a barrel-generator.
One object of the present invention is thus to provide a method for controlling a stepping motor as a result of which the number of rates available for chopping the driving pulses applied to the motor coil can be much higher than when the known method described hereinbefore is used, without the complexity and thus the cost price of the circuit which allows the method to be implemented, being increased too much, the slaving of the quantity of electric energy supplied to the motor coil to the mechanical load driven by the rotor thereof being thus able to be considerably improved and the total electric power consumption of the motor being thus able to be considerably reduced.
This object is achieved by the method whose features are listed in claim
1
annexed hereto.
Another object of the present invention is to propose a control circuit for a stepping method which implements this method.
This object is achieved by the circuit whose features are listed in claim
6
annexed hereto.
As will be explained in detail hereinafter, these features of the method according to the present invention and the device which implements the method allow the number of distinct values which the chopping rate of the driving pulses applied to the motor coil can take to be considerably increased. It follows that the quantity of electric energy which has to be supplied to the coil can be slaved much better to the mechanical load driven by the rotor of the motor, which results, all other things being equal, in a reduction in such quantity of electric energy.
REFERENCES:
patent: 4361410 (1982-11-01), Nakajima et al.
patent: 4467265 (1984-08-01), Antognini et al.
patent: 6034502 (2001-03-01), Buhler
patent: 0 154 889 (1985-09-01), None
patent: 0 676 859 (1995-10-01), None
patent: 2 059 649 (1981-04-01), None
Eta S.A. Fabriques d'Ebauches
Griffin & Szipl, P.C.
Roskoski Bernard
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