Rotor/stator voltage modulation device, in particular for a brus

Electrical generator or motor structure – Dynamoelectric – Rotary

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310 68B, H02K 1100, H02K 1300

Patent

active

054790573

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns the modulation of the current in the phases of a brushless motor, and more generally the modulation of at least two currents as a function of the rotation of a rotor with respect to the stator.
Generally, the switching of the current within the phases of a brushless motor is controlled either by Hall-effect sensors which provide logic signals (on/off) which are directly used for switching the phases, or by a resolver or absolute optical coder providing the relative position of the rotor of the motor with respect to its stator. This solution, which is far more precise, is well suited to motors with a sinusoidal wave shape. It is, however, much more expensive and bulky.


SUMMARY OF THE INVENTION

The aim of the invention is to obtain continuous and precise information on the relative positions of the rotor and stator of a brushless motor, with a view to generating alternating signals intended to control the supply of the phases of the motor, by means of a device which is compact and inexpensive and which, in addition, makes it possible, by processing the signals obtained, to have good quality tachometric information on the rotation speed of the motor.
More generally, an objective of the present invention is to obtain continuous and precise information on the position or relative speed of a rotor with respect to a stator by means of a voltage modulation device which is compact and inexpensive.
For this purpose, the present invention proposes a voltage modulation device embodying: connected at points angularly distributed in alternation with the positive and negative terminals of a DC voltage source and having a resistivity such that its potential varies circumferentially in a periodic fashion between a maximum and minimum value, as well as a plurality of collector tracks centered on the axis and each connected to a respective output terminal; and body rotating about the axis, having a plurality of at least two output brushes, of which there are the same number as the plurality of collector tracks, such that each output brush is adapted to sweep a respective collector track. The rotor also includes a plurality of input brushes, equal in number to the number of output brushes, each input brush being electrically connected to a respective output brush, each input brush being adapted to sweep such an annular signal track with a periodic circumferential variation of potential carried by the stator. The input brushes are disposed so as to take off, during the rotation of the rotor with respect to the stator, potentials with a given electrical phase difference.
It will be appreciated that such a device is a continuous-rotation potentiometer with multiple brushes (i.e. with multiple parallel outputs).
The potentiometer delivers, in parallel, P items of periodic information in the course of the rotation of the rotary drive body, P being equal to the number of output brushes. When this potentiometer is used to control a multiphase brushless motor, having its rotor coupled to that of the motor, the number P is in principle equal to the number of phases of the motor (or to a multiple of this number) and its output terminals are each used to control the current of one of the phases of the motor by means of power electronics of any known appropriate type. If n is the number of pairs of poles in the motor, the above-mentioned periodic data have a frequency which is preferably equal to n (even to a sub-multiple of n) times the frequency of rotation of the motor. By appropriate electronic shaping processing of the signals applied by the output brushes to the collector tracks, the shape of the periodic data coming from the potentiometer (zig-zag shape, sinusoidal or trapezoidal shape in particular) can be adapted in accordance with the destination of the periodic data (control of the motor, measurements of speed, control systems, etc.).
Because of its simplicity, the device of the invention is compact and lightweight.
The formation of the signal or collector tracks uses prov

REFERENCES:
patent: 2151793 (1939-03-01), Patin
patent: 2538415 (1951-01-01), Ergen
patent: 3116431 (1963-12-01), Baudot
patent: 4631540 (1986-12-01), Feldman
patent: 4933585 (1990-06-01), Rossi
patent: 5281880 (1994-01-01), Sakai
Patent Abstracts of Japan, Fujitsu Ltd., Oct. 7, 1982 vol. P p. 187.

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