GB2102955A - Improvements relating to servo systems - Google Patents

Abstract

A servo system is designed to produce an output whereby the relative motion between two members can be followed by an instrument which will indicate their relative positions. A rotary member (1) may have a magnet (3) which cooperates with three Hall effect sensors (2) spaced evenly around the axis of rotation. The outputs of these sensors are amplified (4) and applied to the windings of a D.C. polyphase synchromotor (5), having delta or start connections. In an alternative embodiment (not shown) the motion may be rectilinear with a number of magnets (13) attached to the movable member (11) moving past a row of stationary Hall effect sensors (12). The outputs are used similarly to drive a synchromotor (15). Whilst the described embodiments utilize Hall effect sensors, the use of other (unspecified) galvanomagnetic sensors is suggested. <IMAGE>

Description

SPECIFICATION Improvements relating to servo systems This invention relates to servo systems, and is concerned with the provision of an electrical output corresponding to the relative positions of two members which is used to govern a servo motor.

According to the present invention there is provided a servo system having a transducer for determining the position of one member in relation to another member, comprising a plurality of galvanomagnetic devices on said one member and a magnet on the other member which influences said galvanomagnetic device for the latter to produce a combination of outputs unique to the instantaneous relative positions of said members, and a D.C. polyphase synchromotor with a corresponding plurality of phases to which said outputs are respectively applied, whereby the motor follows the movements of the rotor.

Generally said one member will be movable and the other fixed. The movable one may be rotary or have a linear motion. The galvanomagnetic devices are conveniently Hall effect sensors, and usually there will be three; and for the rotor device they will be equally spaced about the axis. Their outputs will normally be amplified before being applied to the synchromotor.

For a better understanding of the invention some embodiments will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagram of an angular position transducer with an associated servo motor, and Figure 2 is a diagram of a linear position transducer with an associated servo motor.

In Figure 1, a stator 1 of circular form has three Hall effect sensors 2 equally spaced around its periphery. A rotor 3, represented by a diametral bar magnet, rotates partially or completeiy within this array of sensors, whose outputs change according to the angular position of the rotor. The rotor as a whole may be of any form, subject to the requirement that it provides a magnetic field that rotates with it. This may be from a permanent magnet or from an electromagnet. Each sensor output, whose amplitude and sign is dependent on the rotor position, is applied to a respective amplifier 4 and thence to a D.C. polyphase synchromotor 5, whose windings are here shown in delta form. In practice, it may be preferred to have a star connection. The output shaft of this motor will consequently follow the rotation of the rotor 3.

It will be seen that there are three sensors and three windings. It is also possible to have any greater number than three sensors, with a corresponding number of motor phases; but as a matter of practice such numbers will usually be multiples of three, and seldom greater than nine.

Figure 2 shows an equivalent linear transducer and the parts are referenced correspondingly with the addition of 10. Instead of a single magnet 3, however, there are three magnets 13 along a linearly movable shaft at one and a half times the spacing of the adjacent fixed sensors 12. The central magnet has its polarity reversed compared with the two end ones, so that the sensor outputs will match those of Figure 1.

The synchromotor in each case will follow the magnetic element in linear fashion. It would, however, be possible to have a non-uniform spacing of the sensors, giving rise to a non-linear following motion of the motor. This might have application, for example, to the use of the motor in governing a moving-needle indicator, where a non-linear scale might be required.

Claims

1. A servo system having transducer means for determining the position of one member in relation to another member, comprising a plurality of galvanomagnetic devices on said one member and means providing at least one magnetic pole pair on the other member which influences said galvanomagnetic devices for the latter to produce a combination of outputs unique to the instantaneous relative positions of said members, and a D.C. polyphase synchromotor with a corresponding plurality of phases to which said outputs are respectively applied, whereby the motor follows the relative movements of said members.

2. A servo system as claimed in Claim 1, wherein said one member is movable and the other fixed.

3. A servo system as claimed in Claim 2, wherein said one member is rotary.

4. A servo system as claimed in Claim 2, wherein said one member has a linear motion.

5. A servo system as claimed in any preceding claim, wherein the galvanomagnetic devices are Hall effect sensors.

6. A servo system as claimed in claim 5, wherein there are three such sensors.

7. A servo system as claimed in Claim 6 as appendent to Claim 3, wherein the sensors are equally spaced about the axis of rotation.

8. A servo system substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements relating to servo systems This invention relates to servo systems, and is concerned with the provision of an electrical output corresponding to the relative positions of two members which is used to govern a servo motor. According to the present invention there is provided a servo system having a transducer for determining the position of one member in relation to another member, comprising a plurality of galvanomagnetic devices on said one member and a magnet on the other member which influences said galvanomagnetic device for the latter to produce a combination of outputs unique to the instantaneous relative positions of said members, and a D.C. polyphase synchromotor with a corresponding plurality of phases to which said outputs are respectively applied, whereby the motor follows the movements of the rotor. Generally said one member will be movable and the other fixed. The movable one may be rotary or have a linear motion. The galvanomagnetic devices are conveniently Hall effect sensors, and usually there will be three; and for the rotor device they will be equally spaced about the axis. Their outputs will normally be amplified before being applied to the synchromotor. For a better understanding of the invention some embodiments will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagram of an angular position transducer with an associated servo motor, and Figure 2 is a diagram of a linear position transducer with an associated servo motor. In Figure 1, a stator 1 of circular form has three Hall effect sensors 2 equally spaced around its periphery. A rotor 3, represented by a diametral bar magnet, rotates partially or completeiy within this array of sensors, whose outputs change according to the angular position of the rotor. The rotor as a whole may be of any form, subject to the requirement that it provides a magnetic field that rotates with it. This may be from a permanent magnet or from an electromagnet. Each sensor output, whose amplitude and sign is dependent on the rotor position, is applied to a respective amplifier 4 and thence to a D.C. polyphase synchromotor 5, whose windings are here shown in delta form. In practice, it may be preferred to have a star connection. The output shaft of this motor will consequently follow the rotation of the rotor 3. It will be seen that there are three sensors and three windings. It is also possible to have any greater number than three sensors, with a corresponding number of motor phases; but as a matter of practice such numbers will usually be multiples of three, and seldom greater than nine. Figure 2 shows an equivalent linear transducer and the parts are referenced correspondingly with the addition of 10. Instead of a single magnet 3, however, there are three magnets 13 along a linearly movable shaft at one and a half times the spacing of the adjacent fixed sensors 12. The central magnet has its polarity reversed compared with the two end ones, so that the sensor outputs will match those of Figure 1. The synchromotor in each case will follow the magnetic element in linear fashion. It would, however, be possible to have a non-uniform spacing of the sensors, giving rise to a non-linear following motion of the motor. This might have application, for example, to the use of the motor in governing a moving-needle indicator, where a non-linear scale might be required. Claims

1. A servo system having transducer means for determining the position of one member in relation to another member, comprising a plurality of galvanomagnetic devices on said one member and means providing at least one magnetic pole pair on the other member which influences said galvanomagnetic devices for the latter to produce a combination of outputs unique to the instantaneous relative positions of said members, and a D.C. polyphase synchromotor with a corresponding plurality of phases to which said outputs are respectively applied, whereby the motor follows the relative movements of said members.

2. A servo system as claimed in Claim 1, wherein said one member is movable and the other fixed.

3. A servo system as claimed in Claim 2, wherein said one member is rotary.

4. A servo system as claimed in Claim 2, wherein said one member has a linear motion.

5. A servo system as claimed in any preceding claim, wherein the galvanomagnetic devices are Hall effect sensors.

6. A servo system as claimed in claim 5, wherein there are three such sensors.

7. A servo system as claimed in Claim 6 as appendent to Claim 3, wherein the sensors are equally spaced about the axis of rotation.

8. A servo system substantially as hereinbefore described with reference to the accompanying drawing.