GB2159004A - Rotational velocity-type transducer - Google Patents

Abstract

The rotational velocity-type transducer comprises a permanent magnet (1), which is fabricated as a disk provided with poles alternating circle-wise and with an axial opening (2) adapted for a rotary shaft (3). In front of the poles of the permanent magnet (1) there are disposed electronic conductors (7a) of a winding (4a) arranged on a base, which electronic conductors are connected in series through the frontal portions (8a) of the winding (4a). Just like the winding (4a), there is arranged a winding (4b) of which the electronic conductors (7b) and the frontal portions (8b) are mounted closely to the electronic conductors (7a) and the frontal portions (8a) and so that they form the displacement therebetween in the range from 30 to 330 electrical degrees. The taps of the windings (4a, 4b) are connected to a differential amplifier (9) whilst their other taps are linked with a common bus (10) of said amplifier (9).

Description

SPECIFICATION Rate-or-turn transducer Technical Field This invention relates to measuring instruments and, in particular, to rate-of-turn transducers.

Background Art The basic demand associated with measuring instruments and pickups is the accuracy of measurements. The design of pickups and the principle of measurements are selected so that the output is not affected by any distorting factors or noises.

Conventionally, rate-of-turn transducers comprise each a permanent magnet which is a disk having alternating, radially or axially magnetized, poles and a central opening for the shaft, and a winding mounted on a base made of an insulating material.

The number of active conductors is equal to (2n + 1)p where n is an integer, p is the number of poles. These active conductors are placed opposite the poles of the permanent magnet and connected in series by the winding ends (cf., for example, British Patent Application No. 2,022,326, filed May 1979, Class H 02 K 11/00, 16/04,21/00; G Ol P 3/48; and US Patent No. 4,093,897, Class H 02 P 5/06). The winding is connected to the compensating turn in series opposition in these prior art devices in order to eliminate the spurious signal which contributes to the error in determination of the rotational speed. With the same aim in view, the transducer winding is distributed into several sections, each shifted by 180 electrical degrees and connected in series (cf., for example, L.N. Safonov, V.N.Volniansky et al., Pretsizionnye Datchiki Ugla s Pechatnymi Obmotkami, Precision Printed-Winding Angle-Data Transducers. Biblioteka Priborostroitelia, 1977, Mashinostroenie Publ., Moscow, pp.7-13, 560).

As the permanent magnet rotates, the useful signal emf having alternating polarity is induced in the active conductors of the winding. But at the same time external magnetic or electromagnetic fields induce the noise emf in the active conductors and winding front ends. These fields are compensated in the winding active conductors because they are connected in series opposition, while in the winding ends they are added because the winding front ends are connected in series via the active conductors.

To summarize, noise signals are not cancelled completely in prior art rate-of-turn transducers because the compensating turn of the winding is positioned at some distance from the winding ends due to the inherent structure of the winding itself.

This is particularly evident when the external electromagnetic field is not symmetrical as the one produced by a mains transformer. In such transducers, even the noises induced in connecting conductors between the winding and subsequent facilities are not compensated.

Disclosure of the Invention This invention is to provide a rate-of-turn transducer wherein complete cancellation of external noises contributes to a more accurate determination of rotational speed.

There is provided a rate-of-turn transducer comprising a permanent magnet which is a disk having alterriating poles around its circumference and a central opening for a shaft, and a winding placed on a mounting, whose active conductors are positioned opposite the permanent magnet poles and connected in series to the winding front ends, which, according to the invention, also comprises an additional winding whose active conductors and front ends connecting said active conductors in series are arranged similarly to the active conductors and front ends of the main winding, very close to one another and with a displacement of from 30 to 330 electrical degrees, and a differential amplifier whose inputs are connected to some terminals of the main and additional windings, while other terminals thereof are connected to a common supply line of said differential amplifier.

Advisably, the differential amplifier in the rate-ofturn transducer should be made as a voltage comparator.

The rate-of-turn transducer made according to the invention permits extremely accurate determination of rotational speed due to the complete cancellation of electromagnetic noises.

Brief Description of the Drawings The invention will now be described with reference to a specific embodiment thereof, taken in conjunction with the accompanying drawings, wherein: Fig. 1 shows a general view of a rate-of-turn transducer, according to the invention; Fig. 2 shows a section view taken along line Il-Il of Fig.1, according to the invention; Fig. 3 shows an enlarged view of a base part made of an insulating material, windings being placed in the slots of said base, according to the invention; Fig. 4 shows schematically the view of Fig. 3 wherein the directions of electromagnetic noise emf's are indicated, according to the invention; Fig. 5 shows an electric connection diagram of windings and a voltage comparator, according to the invention;; Fig. 6 shows input and output electrical signals of the voltage comparator, according to the invention.

Best Mode For Carrying Out the Invention A rate-of-turn transducer comprises a permanent magnet (Figs. 1 and 2) which is a disk having radially magnetized N and S poles alternating along its circumference. The disk has a central opening 2 to fit a shaft 3. The transducer also comprises windings 4a and 4b placed, in this embodiment, in slots 5 (Fig.

3) of a base 6 made of an insulating material. The windings 4a and 4b are composed of active conductors 7a and 7b connected in series with winding ends 8a and 8b. These active conductors 7a and 7b are positioned opposite the poles of the permanent magnet 1 (Fig. 2) very close to each other, in the same slots. The winding ends 8a (Fig. 3) and 8b are respectively placed very close to each other. The windings 4a and 4b are displaced in relation to each other to an angle lying within a range of from 30 to 330 electrical degrees. These limits are dictated by the permissible output signal level. In this embodiment of the transducer, the windings 4a (Fig. 4) and 4b are displaced by 180 electrical degrees or n/p, where p is the number of poles.In this case such displacement is thought to be optimal.

The rate-of-turn transducer also comprises a differential amplifier 9 (Fig. 1) whose inputs are connected to the like terminals of the windings 4a and 4b, while the other like terminals of the windings 4a and 4b are connected to a common line 10 of the differential amplifier 9. The like terminals, in this context, are either the starts or the ends of the windings.

A voltage comparator 11 (Fig. is used as the differential amplifier in order to obtain a rectangular output signal of the transducer.

In another embodiment of the rate-of-turn transducer, an axially magnetized permanent magnet is used. Here the active conductors of windings are arranged similarly to the above described transducer but in the radial direction.

Printed two-sided circuits can be used to manufacture the transducer windings.

The rate-of-turn transducer made according to the invention operates as follows.

As the permanent magnet 1 (Figs. 1 and 2) rotates, a signal 12 (Fig. 6) is induced in the winding 4a (Fig.

5) coupled to an inverting input of the comparator 11. The frequency of this signal 12 is the function of the rotational speed of the transducer. A signal 3 induced in the winding 4b has the same frequency and amplitude but is out of phase as compared to the signal 12. An amplified rectangular signal 14 is produced at the output of the comparator 11.

In case the transducer is exposed to an external electromagnetic noise field, a noise emf I, is induced in the active conductors 7a (Fig. 4) and 7b, and in the winding ends 8a and 8b. The noise emf's are cancelled out in the active conductors 7a and 7b which are connected in series opposition, while in the winding ends 8a and 8b they are added. In addition, the emf's I, are superimposed on the signals 12 (Fig. 6) and 13 generated by the rotating magnet, are added thereto, and supplied, as the emf lu t to the inputs of the comparator 11 (Fig. 5). Since the noise signal is supplied to the inputs of the comparator in phase, it has no effect on the output signal 14(Fig.6).

To sum up, the effect of external electromagnetic fields can be almost completely cancelled out by introducing two identical windings whose active conductors are displaced to an angle lying within a range of from 30 to 330 electrical degrees and positioned very close to one another as are the winding ends, and a voltage comparator whereto the windings are connected. Noise cancellation makes it possible to improve the accuracy of measuring the rate of turn.

Industrial Applicability The invention is mainly applicable to electric motors used in video and sound recording and reproducing equipment in order to measure and adjust the rotational speed of such motors.

Claims (2)

1. A rate-of-turn transducer comprising a permanent magnet which is a disk having alternating poles arranged along its circumference and a central opening to fit a shaft, and a winding mounted on a base whose active conductors are positioned opposite the permanent magnet poles and connected in series with the winding ends, characterized in that it comprises an additional winding (4b) whose active conductors (7b) and winding ends (8b), providing a series connection of said active conductors (7b), are arranged similarly to the active conductors (7a) and winding ends (8a) of the main winding (4a) very close to each other and displaced within a range of from 30 to 330 electrical degrees, and a differential amplifier (9) whose inputs are connected to some terminals of the main and additional windings (4a and 4b), other terminals thereof being connected to a common supply line (10) of said differential amplifier (9).

2. A rate-of-turn transducer as claimed in claim 1, characterized in that the differential amplifier is made as a voltage comparator (11).