WO1995022741A1

WO1995022741A1 - Sensor apparatus and light unit including such apparatus

Info

Publication number: WO1995022741A1
Application number: PCT/GB1995/000341
Authority: WO
Inventors: Colin Robert Everett; Iain Alexander Hood
Original assignee: Gentech International Limited
Priority date: 1994-02-18
Filing date: 1995-02-17
Publication date: 1995-08-24
Also published as: GB9403147D0

Abstract

Sensor apparatus comprises a housing (1, 1a, 1b, 1c) defining a cavity (2), and a first magnetic member (3) mounted on the housing (1) above the cavity (2). A second magnetic member in the form of two ball bearings (5, 6) is suspended, by magnetic attraction, from the first magnetic member (3) so as to depend into the cavity (2) and is movable in the cavity relative to an axis of the apparatus. The apparatus includes a sensor, such as a reed switch (9), responsive to the magnetic field in the vicinity of the free end of the lower ball bearing (6), for detecting whether the two ball bearings (5, 6) are substantially aligned with the said axis of the apparatus. The apparatus can be used, for example, as a tilt sensor. When used as a tilt sensor, the apparatus can be included within a light unit which is illuminated upon tilting of the unit.

Description

SENSOR APPARATUS AND LIGHT UNIT INCLUDING SUCH APPARATUS

This invention relates to sensor apparatus, and in particular sensor apparatus of the type in which movement of one part of the apparatus relative to another part can be induced by application of an external force, and a sensor that is responsive to the relative positions of the parts of the apparatus. The invention also relates to a light unit including such sensor apparatus. Various sensors of this type have been proposed, a well known example being a mercury tilt switch in which movement of mercury relative to the body of the tilt switch as the body is moved makes or breaks an electrical connection, for example to trigger an alarm.

Other devices with similar operating principles utilise a pendulum of some sort which is normally aligned with a given axis of the device.

When the device is tilted, the pendulum maintains its vertical orientation and so moves relative to the axis of the device, thus triggering a sensor.

According to the present invention there is provided sensor apparatus comprising: a housing defining a cavity; a first magnetic member mounted on the housing above the cavity; a second magnetic member which is suspended, by magnetic attraction, from the first magnetic member so as to depend into the cavity and which is movable in the cavity relative to an axis of the apparatus; and a sensor, responsive to the magnetic field in the vicinity of the free end of the second magnetic member, for detecting whether the second magnetic member is substantially aligned with the said axis of the apparatus.

According to the present invention there is also provided a light unit including a sensor apparatus as set out above, and a lamp activatable by the sensor depending on the alignment of the second magnetic member relative to the axis of the sensor apparatus. The invention provides a particularly simple sensor apparatus in which a pendulum arrangement is provided by suspension of one magnetic member from another, the magnetic attraction maintaining the members in contact with one another while allowing the second magnetic member to move relative to the housing.

When used as a tilt switch, for example, the said axis of the apparatus may be an axis which is vertical under normal conditions so that the second magnetic member is aligned with the axis under normal conditions. However, when the apparatus is tilted, the axis tilts relative to the vertical while the second magnetic member maintains its vertical orientation. The movement of the second magnetic member out of alignment with the axis of the apparatus is detected by the sensor to indicate that the apparatus has been tilted.

For some applications, it may only be necessary to detect movement of the second magnetic member relative to the housing in a given vertical plane, in which case movement of the second magnetic member may be constrained accordingly, for example by appropriate shaping of the cavity. However, the second magnetic member is preferably movable relative to the said axis of the apparatus in any plane containing the axis.

While both the first and second magnetic members could comprise magnets, i.e. magnetised elements, only one magnetic member may comprise a magnet, the other being formed of a magnetisable material. Preferably, the first magnetic member comprises a magnet and the second magnetic member is formed of a magnetisable material. To avoid the possibility of the magnetic members becoming permanently detached from one another in use due to a shock applied to the system, it is advantageous for the housing to be shaped to limit the maximum possible separation of the magnetic members such that, if the magnetic members become separated in use, the magnetic attraction of the members is always sufficient to re-establish contact.

In a preferred arrangement, the second magnetic member comprises first and second balls, the first ball being suspended from the first magnetic member and the second ball being suspended from the first ball by magnetic attraction. The pendulum effect is then achieved by means of a rolling action between the first ball and the first magnetic member and/or between the second ball and the first ball in use. The second ball is preferably larger than the first ball, and each of the first and second balls are preferably formed of a magnetisable material, the first magnetic member comprising a magnet. In embodiments where the second magnetic member is formed by first and second balls, for the reason given above it is preferred that the housing is shaped to limit the maximum possible separation of the first ball and the first magnetic member, and the first and second balls, such that, if the first ball is separated from the first magnetic member or the second ball in use, the magnetic attraction is always sufficient to re-establish contact.

In a particularly convenient arrangement, the first ball is confined by the housing such that the said axis of the apparatus is always substantially aligned with the diameter of the first ball when the first ball is in contact with the first magnetic member. Plus, lateral movement of the first ball relative to the said axis is inhibited in use, the second ball rolling relative to the first ball to provide the pendulum effect. The type of sensor used in the apparatus may of course be varied depending upon, for example, the particular application. However, particularly where the apparatus is used as a tilt switch, the sensor conveniently comprises a reed switch.

When the sensor apparatus is used as a tilt switch, it can be included within a light unit which is illuminated when tilted. The light unit can be used in automotive applications, such as for lighting engine or boot compartments, or in domestic applications such as inclusion in chest freezer lids or the like.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic exploded view, partially cut away, of sensor apparatus embodying the invention;

Figure 2 is a schematic cross-section of the assembled apparatus of Figure 1 along a longitudinal axis of the apparatus; Figure 3 is a schematic cross-section of the apparatus of Figure 1 taken at right angles to the cross-section of Figure 2;

Figure 4 is a schematic perspective view, partially cut away, of a light unit including sensor apparatus, according to another embodiment of the invention; and Figure 5 is an external perspective view, from another side, of the unit shown in Figure .

The sensor apparatus shown in the Figures 1 to 3 comprises a housing 1 consisting of three parts, an upper housing part la, a base lb and a retainer lc. When assembled as shown in Figures 2 and 3. the housing defines a cavity 2. The apparatus includes a first magnetic member in the form of a cylindrical magnet 3 which is polarised through its vertical axis. The magnet 3 is mounted in a recess 4 of the upper housing part la so as to be situated above the cavity 2 in the assembled apparatus. The housing parts may be fixed together, and the magnet 3 secured to the housing, by any convenient means, and the assembled apparatus may be encapsulated if desired. A second magnetic member is provided in the form of two, highly polished, steel ball bearings 5. 6. The first ball bearing 5 is suspended, by magnetic attraction, from the magnet 3- and the second, larger ball bearing 6 is suspended by magnetic attraction from the first ball bearing 5- Thus, the second magnetic member formed of the ball bearings 5 and 6 depends from the magnet 3 into the cavity 2 and acts as a pendulum which is movable relative to a longitudinal axis A-A of the apparatus between the extremes indicated by the broken lines in Figures 2 and 3*

As shown in the figures, the housing 1 is shaped, through provision of a recess 7 in which the first ball bearing 5 is received, to confine the first ball bearing 5 such that lateral movement of the first ball bearing relative to the axis A-A is inhibited, whereby the axis A-A is always aligned along a diameter of the ball bearing 5« The pendulum effect is therefore achieved through a rolling action between the lower ball 6 and upper ball 5 which enables lateral movement of the lower ball 6 relative to the longitudinal axis A-A between the extremes shown in Figures 2 and 3- I will be appreciated that the pendulum is free to move in any plane containing the longitudinal axis A-A.

As can be seen from Figures 2 and 3. the housing 1 is shaped, by means of the inner side walls of the upper housing part la, to limit the maximum lateral or angular movement of the lower ball 6 relative to the longitudinal axis A-A. In this example, the maximum angular displacement is limited to 50°, though with different geometry other angles are of course possible. Also, the retainer lc of the housing 1 is shaped to follow generally the arcuate movement of the pendulum while allowing clearance for the lower ball 6. With the housing shaped in this way, even if the balls 5 and 6 should become detached from each other or from the magnet 3 due to shock, the maximum possible separation of the first ball 5 from the magnet 3 and the second ball 6 is such that the magnetic attraction is always sufficient to re¬ establish contact. Even if the upper ball 5 should become detached from the magnet 3 when the lower ball 6 is at its maximum angular displacement from the axis A-A, the ball 5 cannot pass between the ball 6 and the edge of the recess 7 to drop into the lower portion of the cavity, so the correct configuration is always restored.

Mounted in a recess 8 in the base lb of the housing 1 is a reed switch 9 which is provided with terminal pins 10 formed from the reed switch leads. The terminal pins 10 project through the bottom of the housing 1 for direct PCB mounting in use. The switch is mounted for "end operation", one terminal pin 10 of the reed switch 9 being aligned with the longitudinal axis A-A of the apparatus. It will be appreciated that, since the balls 5. 6 are formed of a magnetisable material, the balls serve to concentrate the magnetic flux from the magnet 3 to provide a polarised field at the free end of the pendulum. With the axis A-A vertical so that the pendulum 5. is aligned with the axis A-A, the magnetic field in the vicinity of the free end of the pendulum is sufficient to hold the reed switch contacts closed. However, if the apparatus is tilted so that the axis A-A moves away from the vertical, a rolling action takes place between the lower and upper balls 6, 5 the lower ball assuming a position vertically below the upper ball at all times and so that the pendulum maintains its vertical orientation. Thus, the pendulum 5» 6 moves away from the axis A-A and the diminished magnetic field at the reed switch contacts causes the switch to be activated, i.e. the contacts to open. The same effect occurs for any direction of tilt.

The precise point at which the switch is activated may of course vary depending upon the particular arrangement and switch sensitivity. However, the apparatus is arranged so that the switch is activated before the maximum angular displacement, here 50°, of the pendulum is reached.

It will be appreciated that the size and mass of the ball bearings 5. 6 and the strength of the magnet 3 may be varied depending upon, for example, the sensitivity required. However, inherent in the above design is a degree of mechanical damping caused by the slight magnetic attraction which exists between the lower ball 6 and the magnetic material of the reed switch 9- This can provide an advantage over, for example, mercury type switches where over-sensitivity may be a problem. The embodiment thus provides a particularly simple and effective tilt switch in which a pendulum effect is achieved by magnetic attraction between a lower magnetic member 5, 6 and an upper magnetic member 3. Use of the ball bearings 5, 6 is particularly cost efficient, since ball bearings which do not meet the strict tolerances generally required for application in roller bearings, and which can therefore be obtained at relatively low cost, may be used.

Figures 4 and 5 show the tilt switch incorporated in a light or lamp unit 20. This has a number of applications, for example in the automotive sector for use in lighting engine or boot compartments in vehicles, rather than using separate switch and lamp assemblies. Other uses include provision in chest freezer lids and the like.

As shown in Figures 4 and 5ι the unit 20 includes an upper housing part 21a, a base and lamp part 21b, and a retainer 21c. When assembled, as shown in Figure 4, the housing defines a cavity 22. A cylindrical magnet 23 is mounted in a recess 24 of the upper housing part 21a, as in the embodiment of Figures 1 to 3« Also, in similar fashion, two steel ball bearings 25, 26 are situated within the cavity 22, the first ball bearing 25 being suspended, by magnetic attraction, from the magnet 23, and the second (larger) ball bearing 26 being suspended by magnetic attraction from the first ball bearing 25. The general arrangement of the retainer 21c, cavity 22, magnet 23, recess 24 and the ball bearings 25, 26 is similar to the embodiment of Figures

1 to 3-

The unit 20 further includes a printed circuit board (PCB) assembly 27 within a recess 28 in the base and lamp part 21b, the PCB assembly 27 carrying a reed switch 29, a lamp 30, other components (if necessary) , and being connected to a two-core cable 31 providing power to the lamp 30 via the reed switch 29. A lamp lens 32 is attached to the base and lamp part 21b, covering and protecting the lamp 30. The unit 20 operates in a similar manner to that of Figures 1 to 3, in that, when the unit is moved out of a certain orientation, for example the vertical (as shown in Figures 4 and 5). the reed switch 29 is activated by change in orientation of the ball bearings 25, 26; in this case, activation of the reed switch 29 causes the lamp 30 to be illuminated.

The sensor apparatus shown in Figures 1 to 3 provides a switching action whereby, depending upon the orientation of the apparatus, either a conductive path or no conductive path is provided between the terminals 10 by virtue of the reed switch 9- Whereas in many applications, the current rating of the reed switch will be sufficient for the load requirements, for higher load switching applications further measures may be necessary. In such cases, rather than provide the direct heavy current switching path, the reed switch 9 may instead provide a switching signal to a primary switching device such as a solid state switch. Operation of the reed switch 9 will then activate and deactivate the solid state switch. In a particularly convenient construction, the solid state switch may be incorporated within the housing of the sensor apparatus. This results in a self-contained heavy load sensor apparatus which merely requires the provision of power leads or terminals (for powering the solid state switch) in addition to the terminals for the switched current path. A similar approach can be taken to the combined unit 10 shown in Figures 4 and 5 if a heavy load capability is to be provided, possibly in addition to the lamp 30.

While the above embodiments have been described with reference to their use as a tilt sensor, other applications may of course be envisaged. For example, the apparatus could be used for acceleration/shock sensing, position sensing or magnetic field sensing, and variations may be made to the apparatus, for example to the type of sensor used, as required for a particular application. It will of course be appreciated that many other variations and modifications may be made to the specific embodiments described above without departing from the scope of the invention.

Claims

CLAI S

1. Sensor apparatus comprising: a housing (1) defining a cavity (2); a first magnetic member (3) mounted on the housing (1) above the cavity (2) ; a second magnetic member (5,6) which is suspended, by magnetic attraction, from the first magnetic member (3) so as to depend into the cavity (2) and which is movable in the cavity relative to an axis of the apparatus; and a sensor (9). responsive to the magnetic field in the vicinity of the free end of the second magnetic member (5,6) , for detecting whether the second magnetic member (5.6) is substantially aligned with the said axis of the apparatus.

2. Apparatus as claimed in claim 1, wherein the second magnetic member (5.6) is movable relative to the said axis of the apparatus in any plane containing the axis.

3- Apparatus as claimed in claim 1 or claim 2, wherein the first magnetic member comprises a magnet (3) and the second magnetic member (5,6) is formed of a magnetisable material.

4. Apparatus as claimed in any preceding claim, wherein the housing (1) is shaped to limit the maximum possible separation of the magnetic members (3,5,6) such that, if the magnetic members (3,5.6) became separated in use, the magnetic attraction of the members (3.5.6) is always sufficient to re-establish contact.

5. Apparatus as claimed in any preceding claim, wherein the second magnetic member comprises first and second balls (5.6), the first ball (5) being suspended from the first magnetic member (3) and the second ball (6) being suspended from the first ball (5) by magnetic attraction.

6. Apparatus as claimed in claim 5 when dependent upon claim 3. wherein each of the first and second balls (5,6) are formed of a magnetisable material.

7. Apparatus as claimed in claim 5 or claim 6, wherein the second ball (6) is larger than the first ball (5).

8. Apparatus as claimed in any one of claims to 7. wherein the housing (1) is shaped to limit the maximum possible separation of the first ball (5) and the first magnetic member (3), and the first and second balls (5.6), such that, if the first ball (5) becomes separated from the first magnetic member (3) or the second ball (6) in use, the magnetic attraction is always sufficient to re-establish contact.

9. Apparatus as claimed in any one of claims 5 to 8, wherein the first ball (5) is confined by the housing (1) such that the said axis of the apparatus is always substantially aligned with a diameter of the first ball (5) when the first ball (5) is in contact with the first magnetic member (3).

10. Apparatus as claimed in any preceding claim, wherein the sensor is a reed switch (9) .

11. Apparatus as claimed in any preceding claim, including a solid state switch activatable by the sensor (9).

12. A light unit including a sensor apparatus as claimed in any preceding claim, and a lamp (30) activatable by the sensor (29) depending on the alignment of the second magnetic member (25,26) relative to the axis of the sensor apparatus.

13. A light unit as claimed in claim 12, wherein the housing (20) of the light unit comprises first and second housing parts (21a,21b) , the first and second magnetic members (23,25,26) being mounted in the first housing part (21a), and the lamp (30) being within the second housing part (21b) .

14. A light unit as claimed in claim 13, comprising a printed circuit board (27) between the first and second housing parts (21a,21b), the sensor (29) and the lamp (30) being mounted on the printed circuit board (27).