GB2157830A - Monitoring the speed of a member using Hall effect devices - Google Patents

Abstract

The speed of movement of a member which makes a to-and-fro movement is monitored. A magnet 14 and a Hall sensor 16 are mounted so that magnetic flux created by the magnet 14 passes in succession through a detection zone 18 and the Hall sensor 16. A vane 26 of electrically-conducting but non-ferromagnetic material is mounted on the operating member so that a constant amount of the vane projects into the detection zone throughout the movement. The output of the Hall sensor depends upon the speed of movement since the magnetic field through the Hall sensor is reduced by eddy currents in the vane. In Fig. 1 the movement is rotary, but linear speeds can be measured in a similar manner using a rectangular vane, Fig. 2 (not shown). <IMAGE>

Description

SPECIFICATION Method of monitoring the speed of movement of an operating member This invention is concerned with a method of monitoring the speed of movement of an operating member which makes a to-and-fro movement. Operating members which make to-and-fro movements are used in a very wide range of machines. Such movements may, for example, be oscillatory about an axis or linear.

For example, both these types of movements are used in glassware forming machines of the individual section type. Glassware forming machines of the individual section type are well known and comprise a number of individual glassware forming units (known as sections) which receive gobs of molten glass from a common source and feed their output to a common conveyor. Each section has a mould arrangement which operates to form parisons and a further mould arrangement which operates to blow the parisons into the shape of glassware containers.In conventional machines, the mould arrangements have mould portions which are moved in an oscillatory motion about a vertical axis to open and close the moulds, a transfer mechanism which transfers parisons from the parison mould arrangement to the blow mould arrangement by making an oscillatory motion through approximately 1 80 C about a horizontal axis, a take out mechanism for removing completed glassware from the blow mould arrangement which makes an oscillatory motion about a horizontal axis, and members which make linear to-and-fro movements to position operating members with respect to the mould arrangements. In some cases, it is desirable to be able to monitor the speed of movement of an operating member as it makes its to-andfro movement.For example, in a glassware forming machine of the individual section type, it is desirable to be able to monitor the speed of movement of those operating members which are involved in carrying molten glass since the molten glass may become deformed if excessive forces due to acceleration and/or centrifugal effects are applied to the glass. Where the operating member makes an oscillatory movement about an axis, a tachometer can be used to monitor the speed of movement but tachometers are relatively expensive, bulky so that they may not be readily incorporated into a machine in all cases, and, where a hostile environment exists as is the case in the vicinity of molten glass, require protection.

It is an object of the present invention to provide a method of monitoring the speed of movement of an operating member which makes a to-and-fro movement which can be adapted for use with a movement that is oscillatory about an axis or with a movement which is linear. It is a further object of the present invention to provide a method of monitoring the speed of movement of an operating member which makes a to-and-fro movement which does require apparatus which is expensive or bulky and which requires less protection from hostile environments than some known apparatuses.

The invention provides a method of monitoring the speed of movement of an operating member which makes a to-and-fro movement, the method comprising counting a magnet and a Hall sensor so that magnetic flux created by the magnet passes in succession through a detection zone and the Hall sensor, mounting a vane of electrically-conducting but non-ferromagnetic material on the operating member for movement therewith, the vane being arranged to extend into the detection zone and having a shape such that the amount of the vane which occupies the detection zone is constant throughout the movement of the operating member, and utilising the output of the Hall sensor to determine the speed of movement of the operating member.

A method according to the last preceding paragraph involves the use of a Hall sensor.

Hall sensors depend on the Hall effect, i.e.

that when a magnetic field is applied perpendicular to a conductor carrying current, a potential difference is observed between points on opposite sides of the conductor, points which in the absence of the field would be at the same potential. A suitable Hall sensor can be obtained from the West German firm, Siemens A.G. under designation FP 210 L100. The vane used in the aforementioned method is moving in a magnetic field created by the magnet and, hence, electrical eddy currents are created in the vane which tend to reduce the magnetic field and this reduction in the magnetic field is detected by a reduction in the output of the Hall sensor.

The reduction in the output of the Hall sensor is proportional to the speed of movement of the vane so that the speed of movement can be detected from the output of the Hall sensor. The method can be adapted to either a oscillatory movement about an axis or to linear movement and does not involve apparatus which is expensive or bulky or which requires a great degree of protection from hostile environments.

Where the operating member makes an oscillating movement about an axis, the vane may be a circular disc centred on said axis.

Alternatively, where the operating member is making a linear movement, the vane may be a rectangular plate.

The vane may be suitably made of copper or aluminium and the detection zone, the magnet, and the Hall sensor may be connected by magnet flux conductors made of ferromagnetic but not permanently magnetisable material which define the path of the flux.

The magnet may be a permanent magnet or, if desired, an electro-magnet.

There now follows a detailed description, to be read with reference to the accompanying drawings, of two illustrative methods of monitoring the speed of movement of an operating member which makes a to-and-fro movement.

It is to be understood that the illustrative methods have been selected for description by way of example and not of limitation of the invention.

In the drawings: Figure 1 is a diagrammatic side-elevational view of an apparatus used to carry out the first illustrative method; and Figure 2 is a diagrammatic side-elevational view of an apparatus used to carry out the second illustrative method.

The first illustrative method is a method of monitoring the speed of movement of an operating member which makes an oscillatory to-and-fro movement about an axis 10. A shaft 12 extends along the axis 10 and carries the operating member (not shown). A permanent magnet 14 is mounted adjacent to the shaft 12 as is a Hall sensor 16. The magnet 14 is arranged so that the magnetic flux created thereby passes in succession through a detection zone 18 and the Hall sensor 16.

As shown in Fig. 1, a magnetic flux conductor 20 which is L-shaped connects one end of the detection zone 1 8 to one pole of the magnet 14, a flux conductor 22 which is also Lshaped connects the opposite pole of the magnet 14 to the Hall sensor 16, and a flux conductor 24 which is generally U-shaped connects the Hall sensor 1 6 to the opposite side of the detection zone 1 8 from the conductor 20. The magnetic flux conductors 20, 22 and 24 are made of ferromagnetic but not permanently magnetisable material for example soft iron or ferrocube (which is iron particles in ceramic). The flux conductors 20, 22 and 24 serve to define the path of the magnetic flux between the poles of the magnets 14 via the detection zone 1 8 and the Hall sensor 16.

A vane 26 of electrically-conducting but non-ferromagnetic material such as copper or aluminium is mounted on the shaft 1 2 for movement therewith. Thus, the vane 26 is movable with the operating member and movement of the vane 26 corresponds to movement of the operating member. The vane 26 is circular and of constant thickness with its centre lying on the axis 10. The vane 26, as shown in Fig. 1, is arranged to extend into the detection zone 1 8 and, because of its shape, the amount of the vane 26 which occupies the detection zone 1 8 is constant throughout the movement of the operating member about the axis 10.

In the first illustrative method, after mounting of the components described above, the output of the Hall sensor 1 6 is utilised to determine the speed of movement of the operating member. As the operating member turns about the axis 10, the vane 26 moves through the magnetic field in the detection zone which is created by the magnet 14 and electrical eddy currents are created in the vane 26 which reduce the magnetic field which passes through the Hall sensor 1 6 so that the output of the Hall sensor 1 6 is reduced. The greater the speed of movement of the vane 26, the smaller is the output of the Hall sensor 1 6 so that the speed of movement of the vane 26 and, therefore, of the operating member can be detected from the output of the Hall sensor.

The second illustrative method is a method of monitoring the speed of movement of an operating member which makes a linear toand-fro movement. The method comprises mounting a magnet 44 and a Hall sensor 46 so that the Hall sensor 46 abuts one pole of the magnet 44 and the other pole of the magnet 44 is adjacent one end of a detection zone 46. The opposite side of the Hall sensor 46 is connected by means of a flux conductor 50 made of similar material to the flux conductors 20, 22 and 24 described above. The flux conductor 50 leads to a position on the opposite side of the detection zone 48 from the other pole of the magnet 44. The arrangement is such that the magnet flux created by the magnet 44 passes in succession through the detection zone 48 and the Hall sensor 46, the flux conductor 50 serving to define the path of the flux between the Hall sensor 46 and the detection zone 48.

The second illustrative method also comprises mounting a vane 56 of electricallyconducting but non-ferromagnetic material on the operating member for movement therewith. The vane 56 is made of copper or aluminium and is rectangular and of uniform cross section along its length. In Fig. 2, the vane 56 is shown in cross-section and its path of movement is into and out of the plane of the paper. The vane 56 extends along the direction of movement through the detection zone 48. Thus the vane 56 extends into the detection zone and has a shape such that the amount of the vane which occupies the detection zone 48 is constant throughout the movement of the operating member.

In the second illustrative method the output of the Hall sensor 46 is utilized to determine the speed of movement of the operating member by determining the speed of movement of the vane 56. As the vane 56 passes through the detection zone 48, eddy currents are created in the vane 56 which serve to oppose the magnetic field created by the magnet 44 in the detection zone 48. Variations in the magnetic field are proportional to the speed of movement of the vane 56 and appear as reductions in the output of the Hall sensor 46.

Claims (6)

1. A method of monitoring the speed of movement of an operating member which makes a to-and-fro movement, the method comprising mounting a magnet and a Hall sensor so that magnetic flux created by the magnet passes in succession through a detection zone and the Hall sensor, mounting a vane of electrically-conducting but non-ferromagnetic material on the operating member for movement therewith, the vane being arranged to extend into the detection zone and having a shape such that the amount of the vane which occupies the detection zone is constant throughout the movement of the operating member, and utilising the output of the Hall sensor to determine the speed of movement of the operating member.

2. A method according to claim 1, wherein the operating member makes an oscillating movement about an axis, and the vane is a circular disc centred on said axis.

3. A method according to claim 1, wherein the operating member makes a linear movement and the vane is a rectangular plate.

4. A method according to any one of the claims 1 to 3, wherein the detection zone, the magnet, and the Hall sensor are connected by one or more magnetic flux conductors made of ferromagnetic but not permanently magnetisable material which define the path of the flux.

5. A method of monitoring the speed of movement of an operating member substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

6. A method of monitoring the speed of movement of an operating member substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.