WO2002058023A1

WO2002058023A1 - Motion sensor

Info

Publication number: WO2002058023A1
Application number: PCT/ZA2002/000007
Authority: WO
Inventors: Paul Viranyi
Original assignee: Paul Viranyi
Priority date: 2001-01-22
Filing date: 2002-01-22
Publication date: 2002-07-25

Abstract

A motion sensor (10) which comprises a pair of contacts (12, 14) assembled at right angles to one another so that they bound a spherical cavity which has a ball (34) therein. The ball (34) forms an electrical bridge with contacts (12, 14) when the motion sensor (10) is fitted into an electrical circuit. Movement of the motion sensor (10) results in movement of the ball (34) relative to the contacts (12, 14) and, due to the relative surface roughness of the ball (34) and the contacts (12, 14), the resistance, and thus the current, in the electrical circuit varies. The change in current flowing in the electrical circuit can be detected by electronic means and used to activate an alarm.

Description

MOTION SENSOR

FIELD OF THE INVENTION

THIS INVENTION relates to a motion sensor.

BACKGROUND TO THE INVENTION

The most common form of motion sensor is one that includes an

electrically conductive element which opens or closes an electrical circuit when the

sensor is moved from the position it occupies whilst the circuit in which it is

incorporated is activated or armed. In a first situation, the sensor is armed whilst the

electrical circuit is closed. Subsequent movement of the sensor, sufficient to shift

said element, opens the electrical circuit which causes, for example, an alarm to be

activated. In a second situation, the sensor is armed whilst the electrical circuit is

open. Subsequent movement of the sensor closes the electrical circuit.

However, a disadvantage of most known motion sensors of this type is

that it is possible to prevent the alarm from being activated by carefully moving the

motion sensor whilst maintaining it in the same spacial position it occupied when it

was armed, thereby preventing the conductive element from shifting.

To overcome this problem sensors which have an unbroken electrical

circuit through them have been developed. A minute current constantly flows through the sensor. These sensors operate on the basis that metal is, at microscopic

level, rough. The electrical resistance in the circuit thus varies when one metallic

element of the circuit moves with respect to another.

In one form known to applicant a cylindrical metal casing contains an

axially extending rod which has two spaced apart discs thereon. The rod and casing

are electrically insulated from one another. There is a ball in the annular space

between the rod and the casing, the ball being confined in the space by the discs.

The ball, except when the rod happens to be horizontal which would be an

exceptional event, lies against one of the discs. It thus connects the rod to the

casing. If the sensor is tilted the ball rolls around the casing and the resistance

varies.

This unit can react slowly to movement and has the disadvantage of

being of a size which does not lend itself to surface mounting on a PC board.

Another known form has a casing which is cylindrical and closed at the

lower end by a conical end cap. There is an axial rod in the casing and a ball in the

space between the rod and the casing. The conical end cap causes the ball to roll

towards the centre so that it always touches the rod and the end cap. This sensor is

also too large for surface mounting and can in some circumstances react very

slowly. The present invention seeks to provide a motion senor which can be

surface mounted on a PC board and which has a faster reaction time.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided a

motion sensor comprising a pair of contacts, each of which has a circular portion,

said contacts being assembled at right angles to one another so that they bound a

spherical cavity which has an electrically conductive ball therein, to form an electrical

bridge between said contacts.

In the preferred form, each circular portion has a gap therein, the

circular portion of each contact passing with clearance through the gap of the

circular portion of the other contact.

To enable electrical connections to be made to said circular portions,

there can be an element which protrudes radially outwardly from the circular portion

of said element.

Said elements and gaps can be diametrically opposed.

The assembled contacts can be in a spherical housing of electrically

insulating material. To locate the contacts with respect to the housing there can be

inter-engaging notches and protrusions. In the preferred form, the protrusions protrude radially outwardly from the circular portions and the notches are in the

housing.

In a specific form of the present invention one of said contacts includes

a further circular portion with a gap therein, said gaps being at right angles with

respect to one another and there being a third contact which has a circular portion

with a gap therein, the circular portion of the third contact passing with clearance

through the gap of the further circular portion of said one contact, to define a further

spherical cavity, there being a further electrically conductive ball in said further

cavity.

According to a further aspect of the present invention there is provided

a motion sensor comprising a tube constituted by first and second components,

which are each in the form of a cylinder having a cylindrical wall and an end wall at

one end of the cylindrical wall, the components being open at the ends thereof

opposite to the end wall, the free ends of the cylindrical walls of the components

being spaced apart and bounding a cavity having therein balls which rest on one

another and form an electrical bridge between said components when the sensor is

positioned with said cylindrical walls vertical.

Preferably there are two balls contained in said cavity.

Said end walls can be domed so that the balls are caused to roll outwardly towards said cylindrical walls.

Said components can be joined by an open ended sleeve of

electrically insulating material.

Said cylindrical walls can increase in internal diameter with increasing

distance from the respective end wall.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how

the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a plan view of the three electrically conductive contacts of a

motion sensor;

Figure 2 is a side elevation of the contacts of Figure 1 ;

Figure 3 is a pictorial view of two of the contacts shown in Figures 1 and 2;

Figure 4 is a plan view of one of the two electrical contacts shown in Figure 1 ;

Figure 5 is a view similar to that of Figure 3 and also shows a ball and part of

a housing;

Figure 6 is a section through another form of motion sensor;

Figure 7 is a plan view of a further form of motion sensor;

Figure 8 is an end view of the motion sensor of Figure 7;

Figure 9 is a plan view of a contact of the motion sensor of Figure 7; and Figure 10 is a plan view of the motion sensor of Figure 7.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Figures 1 to 5, the motion sensor illustrated is

generally designated 10 and comprises a first contact 12 and a second contact 14

which are assembled at right angles to one another so as to bound a spherical

cavity 16.

Referring particularly to Figure 4, the contacts 12, 14 each comprise a

circular portion 18 and an elongate element 20 which protrudes radially outwardly

from the circumference of the circular portion 18. The circular portion 18 consists of

two arcuate sections 18.1 and 18.2 which bound a space 22. The sections 18.1 and

18.2 terminate at the left hand end, as viewed in Figure 4, in such manner as to

provide a gap 24 which communicates with the space 22.

The motion sensor 10 further includes a two part housing of electrically

insulating material. One part of the housing is shown in Figure 5 and is designated

26. The housing part 26 is in the form of a hollow hemisphere. The other housing

part is of the same configuration. When joined to one another around their equators

the housing parts form a hollow sphere containing the contacts 12, 14. The

elements 20 protrude from the spherical housing to enable the motion sensor 10 to

be connected into an electrical circuit by, for example, being surface mounted on a

PC board. During assembly, the contacts 12, 14 are interlinked at right angles to

one another. This is shown in Figures 3 and 5. The configuration is such that the

point where the sections 18.1 and 18.2 of the circular portion 18 of each contact 12,

14 join the element 20 of that contact is located within the gap 24 of the other

circular portion 18. Air gaps 28 remain between the contacts 12, 14 to prevent the

contacts 12, 14 touching one another. To ensure that the contacts 12, 14 are

correctly located with respect to one another, diametrically opposed protrusions 30

(Figures 1 , 2 and 4) are provided on each contact 12, 14. The protrusions 30 are

not shown in Figures 3 and 5. The housing parts have corresponding notches 32

(Figure 5) which receive two of the protrusions 30 and these locate one of the

contacts 12, 14. At the poles of the spherical housing there are internal notches (not

illustrated) which receive the other protrusions 30 and locate the other contact 12,

14.

As shown in Figures 1 and 2, a ball 34, of metal or other suitable

electrically conducting material, is located within the cavity 16. The contacts 12, 14

and the ball 34 constitute the three electrically conductive contacts of the motion

sensor 10. The ball 34 permanently connects the contacts 12 and 14 to one another

and thereby completes the circuit through the sensor 10. The gap between the ball

34 and the contacts 12, 14 is shown exaggerated in Figures 1 and 2. The external

circuit in which the sensor 10 is fitted comprises a power supply (not shown), the

contact 12, the ball 34, the contact 14, and electronic means (not shown) for

detecting changes in the current flowing in the circuit. The surfaces of the contacts 12, 14 and ball 34 are, at microscopic

level, uneven. The resistance in the circuit depends on the surface areas of the ball

34 and contacts 12, 14 which are touching. Any movement of the ball 34 changes

the contact area, and hence the resistance, and the change in resistance results in a

change in current which is detected by said electronic means.

Referring now to Figure 6, another form of motion sensor is illustrated.

The motion sensor, generally designated 36, comprises electrical contacts 38 and

40, a synthetic plastics material sleeve 42 and two electrically conducting balls 44,

46. The contacts 38, 40 each comprise a cylindrical side wall 48 and an end wall

50.

The contact 38 bounds a space 52 which is open at the top, as viewed

in Figure 6, and the contact 40 bounds a space 54 which is open at the bottom as

viewed in Figure 6. The electrical contacts 38, 40 are assembled such that the

spaces 52, 54 are placed in communication and form a cavity bounded by the side

walls 48 and the end walls 50 of the contacts 38, 40. The end walls 50 are cone-

shaped and extend inwardly into the cavity.

The sensor of Figure 6 can be mounted vertically. Preferably it is

surface mounted on a PC board by soldering one of the contacts 38, 40 to the

board. The balls 44, 46, when the sensor 36 is vertical, lie as shown in Figure

6. Any movement of the sensor 36 causes the balls 44, 46 to roll around the

sensor's vertical axis relative to one another. Movement of the balls 44, 46 results in

a change in the resistance of the electrical circuit due to the varying contact area as

a result of the relative surface roughness of the balls 44, 46 and contacts 38, 40.

If the sensor 36 is moved to a horizontal position, the balls 44, 46 can

separate. To counter this, one sensor 36 can be mounted with its axis at right

angles to the axis of another sensor 36. This ensures that any motion results in a

change of resistance of at least one sensor 36 when the sensor 36 lies horizontally.

Another method of preventing the balls 44, 46 from separating is to

bell-mouth the side walls 48 of the contacts 38, 40 so that they increase in internal

diameter with increasing distance from the end walls 50. The balls 44, 46 thus tend

to roll down the side walls 48 towards the centre of the sensor 36.

Referring now to Figures 7 to 10, a further motion sensor is illustrated.

The motion sensor, generally designated 56, comprises a tubular casing 58 which

contains a first contact 60, a second contact 62, a third contact 64 and balls 66 and

68.

The contacts 62 and 64 are similar to the contacts 12 and 14, except

that the protrusions 30 have been omitted. The balls 66 and 68 are similar to the balls 44 and 46 (see Figure 6) and are also manufactured from metal or other

suitable electrically conducting material.

The contact 60 (see Figure 9) consists of a main portion 70 and

arcuate sections 72, 74, 76. The main portion 70 and the arcuate section 72 bound

a space 78, and the main portion 70 and the arcuate sections 74 and 76 bound a

space 80. A gap 82 is provided between the main portion 70 and the arcuate

section 72 and, similarly, a gap 84 is provided between the arcuate sections 74 and

76.

To assemble the sensor, the contacts 62 and 64 are placed into the

upwardly open cups of the lower half of the tubular casing 58 and positioned at right

angles to one another. By slightly inclining the contacts it is possible to roll the balls

into the circular portions of the contacts 62, 64. The penultimate step is to

manipulate the contacts 62, 64 so that the contact 60 can be slid into place. The top

half of the casing 62 is then positioned and the casing parts welded togther.

The balls 66 and 68 permanently connect the contact 62 and contact

60 to one another and, similarly, permanently connect the contact 64 and contact 60

to one another, thereby completing the circuit. The air gaps 86 between the balls 66

and 68 and the contacts 62 and 64 is shown exaggerated in Figure 10. The circuit

in which the sensor 56 is fitted comprises a power supply (not shown), the contacts

62 and 64, the balls 66 and 68, the contact 60, and electronic means (not shown) for detecting changes in the current flowing in the circuit.

The surfaces of the contacts 62, 64 and the balls 66, 68 are, at

microscopic level, uneven. The resistance in the circuit depends on the surface

areas of the balls 66, 68 and contacts 60, 62, 64 which are touching. Any

movement of either ball 66, 68 changes the contact area, and hence the resistance,

and the change in resistance results in a change in current which is detected by said

electronic means.

The advantage of this embodiment of the present invention is that one

of the balls 66, 68 is always on a surface which curves generally in the direction in which the motion sensor 56 is tilted. The sensor thus reacts quickly to tilting

movement in almost all directions.

Claims

CLAIMS:

1. A motion sensor comprising a pair of contacts, each of which has a

circular portion, said contacts being assembled at right angles to one another so that

they bound a spherical cavity which has an electrically conductive ball therein to

form an electrical bridge between said contacts.

2. A motion sensor as claimed in claim 1 , wherein each circular portion

has a gap therein, the circular portion of each contact passing with clearance

through the gap of the circular portion of the other contact.

3. A motion sensor as claimed in claim 2, wherein each contact includes

an element which protrudes radially outwardly from the circular portion thereof to

enable electrical connections to be made to said circular portions.

4. A motion sensor as claimed in claim 3, wherein said elements and

gaps are diametrically opposed.

5. A motion sensor as claimed in claim 2, wherein one of said contacts

includes a further circular portion with a gap therein, said gaps being at right angles

with respect to one another and there being a third contact which has a circular

portion with a gap therein, the circular portion of the third contact passing with

clearance through the gap of the further circular portion of said one contact, to define a further spherical cavity, there being a further electrically conductive ball in

said further cavity.

6. A motion sensor comprising a tube constituted by first and second

electrically conductive components, which are each in the form of a cylinder having a

cylindrical wall and an end wall at one end of the cylindrical wall, the components

being open at the ends thereof opposite to the end wall, the free ends of the

cylindrical walls of the components being spaced apart and the components

bounding a cavity having therein electrically conductive balls which rest on one

positioned with said cylindrical walls vertical.

7. A motion sensor as claimed in claim 6, wherein said cavity contains

two balls.

8. A motion sensor as claimed in claims 6 or 7, wherein said end walls

are domed so that any ball which is resting on one of the end walls is caused to roll

outwardly towards said cylindrical walls.

9. A motion sensor as claimed in claims 6 or 7, wherein said components

are joined by an open ended sleeve of electrically insulating material.

10. A motion sensor as claimed in claims 6 or 7, wherein said cylindrical walls each increase in internal diameter with increasing distance from the respective

end wall.