GB1576323A - Instruments responsive to acceleration - Google Patents

Description

(54) INIPROVEMENTS IN OR RELATING TO INSTRUMENTS RESPONSIVE TO ACCELERATION (71) I, SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to instruments of the type responsive to acceleration.

Instruments responsive to acceleration, known, when they measure acceleration as accelerometers, are useful for a variety of purposes. Accelerometers sensitive to and measuring acceleration in the vertical plane are commonly fitted to modern high performance, aircraft and such accelerometers are usually robust and expensive instruments designed to last for a considerable period without maintenance.

There is, however, a requirement for cheaper instruments for use, for example, in the control systems of guided weapons, where they might be expected to be used only once, or in systems for checking the braking efficiencies of motor vehicles.

The present invention supplies an extremely cheap and simple instrument which when connected to a suitable electrical circuit is responsive to acceleration. The instrument is based on the polarised moving iron instruments commonly used as ammeters and voltmeters in the automobile industry. In these instruments a rotatable armature formed of a magnetisable material such as soft iron is sited close to a permanent magnet, by which it becomes polarised.

A coil for passing electrical current is sited adjacent to the armature. A pointer secured to the armature reads on a scale, the elements of the instrument being so arranged that when no current is passing through the coil a zero reading is indicated. When a current passes through the coil a magnetic field is set up which acts on the polarised armature so causing movement of the armature and hence of the pointer.

The amount of rotation of the armature is a function of the current passing through the coil, and hence the instrument can be calibrated as an ammeter or as a voltmeter depending on the circuit arrangement.

According to the present invention, a polarised moving metal instrument which, when suitably aligned and when connected to suitable electric circuitry, is responsive to acceleration and which has a rotatable magnetisable armature adjacent to and magnetised by a permanent magnet, and a coil adjacent to the armature such that when an electric current is passed therethrough a magnetic field is set up tending to rotate the armature, includes an electrically conducting lever having a first end secured to the armature and a second end having a mass attached thereto such that any acceleration of the instrument having a component acting in the plane of rotation of the lever other than along the length of the lever tends to rotate the lever and hence the armature, and two contacts lying in the plane of rotation of the lever one on each side of the lever.

It will be appreciated that acceleration forces acting on the mass, in the plane of rotation of the lever, will cause the mass to move until the lever contacts one or other of the contacts. In use as an accelerometer the instrument is so wired that when the lever touches one of the contacts current is supplied to the coil in such a sense that the armature tis rotated to separate the contact and lever. In practice, during acceleration, the mass, lever and armature will vibrate repeatedly making and breaking touch with the contact. By suitably processing the current supplied to the coil a reading in terms of, for example, acceleration can be presented.

One embodiment of the invention will now be described, by way of example only, with reference to the diagrammatic drawings accompanying the Provisional Specification of which: Figure 1 is an elevation in section of an instrument according to the invention wired to give a display in terms of distance travelled, and Figure 2 is a plan view along the lines lI-ll of Figure 1 of part of the instrument.

An armature 10 of magnetisable material such as soft iron is rotatably mounted between arms 11 of a mounting 12 secured to a casing 13. Adjacent to the armature 10 is a permanent magnet 14 which may be formed, for example, of cobalt-steel. Due to the presence of the magnet 14 the armature 10 is polarised, a south pole appearing adjacent to the north pole of the permanent magnet 14 and vice versa, as indicated in Figure 1. Also adjacent to the armature 10 is a coil 15 connected to terminals 16, 17 on the casing 13. Secured to the armature 10, is a lever 18 at the end of which is mounted a mass 19. Projecting inwardly from terminals 20, 21 on the casing 13 are contacts 22. 23, one on either side of the lever 18. The disposition of the components of the instrument is such that the lever 18 does not touch either of the contacts 22 or 23, but that rotation of the armature 10 causes the lever 18 to touch one or other of the contacts. The lever 18, armature 10, mounting means and mounting 12 are electrically conducting, and the mounting 12 is connected to a terminal 24 on the casing 13. Terminal 24 is connected to earth, and terminals 20, 21 are connected to a balanced input circuit 25. When the lever 18 touches one of the contacts 22, 23 an electrical circuit is completed, and the balanced input circuit 25 provides an input to the terminals 16, 17 and hence to the coil 15. Current in the coil 15 sets up a magnetic field which acts on the armature 10 to rotate it in such a sense that the lever 18 is moved away from the contact 22 or 23. The balanced input circuit 25 also provides an input for an analogue circuit in the form of a double integration circuit 26 which provides an input for a distance travelled indicator 27.

In use the instrument is mounted in a carrier so that acceleration forces along the intended direction of motion of the carrier act at right angles to and in the plane of rotation of the lever 18. As the carrier moves from rest acceleration forces are set up, and these act on the mass 19 to rotate the lever 18 and armature 10 until the lever 18 touches one or other of the contacts 22, 23. As soon as the lever 18 touches one of the contacts the balanced input circuit provides current to the coil 15, setting up a magnetic field which causes the armature 10 to rotate and move the lever 18 out of touch with the contact. This results in cutting off of the current to the coil 15, and whilst acceleration forces persist the mass 19 and hence lever 18 and armature 10 will immediately rotate until the lever 18 again touches the contact. This sequence of events will continue as long as acceleration forces persist. In synchronism with passing current to the coil 15 the balanced input circuit 25 passes signals and provides an output to the dial 27 which indicates distance travelled.

It will be realised that whilst the above described embodiment of the invention is used for recording distance travelled, by suitable circuitry readings of acceleration or of velocity can be produced. Design of suitable circuits for performing the various tasks are a matter of routine, and will not be described in detail here. The use of polarised moving metal instruments as ammeters and voltmeters is well known, so the choice of coils 15 and magnets 14 for instruments for a particular use according to this invention will again be a matter of routine.

Whilst, in the embodiment described above with reference to Figures 1 and 2 the instrument is described as being installed in a carrier in such a manner that acceleration forces act on the mass 19 in a direction normal to the lever 18 when in the null position, and in the plane of rotation of the lever 18, this arrangement may not always be possible. Provided the direction of action of the acceleration forces is known, accurate results can still be obtained by suitable design of the electric circuitry.

Small divergences fo the direction of action of the forces from the design directions should have little effect on accuracy.

It will be apparent that, in the instrument described above with reference to Figures 1 and 2 the lever 18 will tend to move into a position where it rests against one or other of the contacts 22, 23. This will not affect the readings, provided that switching on of the electrical power supply is synchronous with the start of the acceleration to be measured. If this is not practicable, the instrument may be so arranged that the lever 18 is suspended below the armature 10; the lever 18 may be centralised by, for example, one or more light springs (having spring stiffnesses negligible relative to the expected acceleration forces); or the lever may be centralised by one or more removable stops which are removed to allow measurement to begin.

Alternatively the electronic circuits can be arranged to ignore any standing currents until a preset acceleration force is exceeded.

WHAT I CLAIM IS:- 1. A polarised moving metal instrument

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

Claims (11)

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

   now be described, by way of example only, with reference to the diagrammatic drawings accompanying the Provisional Specification of which: Figure 1 is an elevation in section of an instrument according to the invention wired to give a display in terms of distance travelled, and Figure 2 is a plan view along the lines lI-ll of Figure 1 of part of the instrument.

   An armature 10 of magnetisable material such as soft iron is rotatably mounted between arms 11 of a mounting 12 secured to a casing 13. Adjacent to the armature 10 is a permanent magnet 14 which may be formed, for example, of cobalt-steel. Due to the presence of the magnet 14 the armature 10 is polarised, a south pole appearing adjacent to the north pole of the permanent magnet 14 and vice versa, as indicated in Figure 1. Also adjacent to the armature 10 is a coil 15 connected to terminals 16, 17 on the casing 13. Secured to the armature 10, is a lever 18 at the end of which is mounted a mass 19. Projecting inwardly from terminals 20, 21 on the casing 13 are contacts 22. 23, one on either side of the lever 18. The disposition of the components of the instrument is such that the lever 18 does not touch either of the contacts 22 or 23, but that rotation of the armature 10 causes the lever 18 to touch one or other of the contacts. The lever 18, armature 10, mounting means and mounting 12 are electrically conducting, and the mounting

   12 is connected to a terminal 24 on the casing 13. Terminal 24 is connected to earth, and terminals 20, 21 are connected to a balanced input circuit 25. When the lever 18 touches one of the contacts 22, 23 an electrical circuit is completed, and the balanced input circuit 25 provides an input to the terminals 16, 17 and hence to the coil 15. Current in the coil 15 sets up a magnetic field which acts on the armature 10 to rotate it in such a sense that the lever 18 is moved away from the contact 22 or 23. The balanced input circuit 25 also provides an input for an analogue circuit in the form of a double integration circuit 26 which provides an input for a distance travelled indicator 27.

   In use the instrument is mounted in a carrier so that acceleration forces along the intended direction of motion of the carrier act at right angles to and in the plane of rotation of the lever 18. As the carrier moves from rest acceleration forces are set up, and these act on the mass 19 to rotate the lever 18 and armature 10 until the lever 18 touches one or other of the contacts 22, 23. As soon as the lever 18 touches one of the contacts the balanced input circuit provides current to the coil 15, setting up a magnetic field which causes the armature 10 to rotate and move the lever 18 out of touch with the contact. This results in cutting off of the current to the coil 15, and whilst acceleration forces persist the mass 19 and hence lever 18 and armature 10 will immediately rotate until the lever 18 again touches the contact. This sequence of events will continue as long as acceleration forces persist. In synchronism with passing current to the coil 15 the balanced input circuit 25 passes signals and provides an output to the dial 27 which indicates distance travelled.

   It will be realised that whilst the above described embodiment of the invention is used for recording distance travelled, by suitable circuitry readings of acceleration or of velocity can be produced. Design of suitable circuits for performing the various tasks are a matter of routine, and will not be described in detail here. The use of polarised moving metal instruments as ammeters and voltmeters is well known, so the choice of coils 15 and magnets 14 for instruments for a particular use according to this invention will again be a matter of routine.

   Whilst, in the embodiment described above with reference to Figures 1 and 2 the instrument is described as being installed in a carrier in such a manner that acceleration forces act on the mass 19 in a direction normal to the lever 18 when in the null position, and in the plane of rotation of the lever 18, this arrangement may not always be possible. Provided the direction of action of the acceleration forces is known, accurate results can still be obtained by suitable design of the electric circuitry.

   Small divergences fo the direction of action of the forces from the design directions should have little effect on accuracy.

   It will be apparent that, in the instrument described above with reference to Figures 1 and 2 the lever 18 will tend to move into a position where it rests against one or other of the contacts 22, 23. This will not affect the readings, provided that switching on of the electrical power supply is synchronous with the start of the acceleration to be measured. If this is not practicable, the instrument may be so arranged that the lever 18 is suspended below the armature 10; the lever 18 may be centralised by, for example, one or more light springs (having spring stiffnesses negligible relative to the expected acceleration forces); or the lever may be centralised by one or more removable stops which are removed to allow measurement to begin.

   Alternatively the electronic circuits can be arranged to ignore any standing currents until a preset acceleration force is exceeded.

   WHAT I CLAIM IS:- 1. A polarised moving metal instrument

   which, when suitably aligned and when connected to suitable electric circuitry, is responsive to acceleration and which has a rotatable magnetisable armature adjacent to and magnetised by a permanent magnet, and a coil adjacent to the armature such that when an electric current is passed therethrough a magnetic field is set up tending to rotate the armature, the instrument including an electrically conducting lever having a first end secured to the armature and a second end having a mass attached thereto such that any acceleration of the instrument having a component acting in the plane of rotation of the lever other than along the length of the lever tends to rotate the lever and hence the armature, and two contacts lying in the plane of rotation of the lever one on each side of the lever.
2. 2. An instrument as claimed in claim 1 in association with electrical circuitry and an electrical power supply such that contact betwen the lever and either of the contacts completes an electrical circuit which results in the supply of electric current to the coil in such a sense that a magnetic field is set up which rotates the armature to move the lever out of contact with the contact.
3. 3. An instrument and electrical circuitry as claimed in claim 2 including means for providing an output of a required parameter.
4. 4. An instrument and electrical circuitry as claimed in claim 3 wherein the means includes an analogue circuit.
5. 5. An instrument and electrical circuitry as claimed in claim 4 or in claim 4 wherein the parameter is acceleration.
6. 6. An instrument and electrical circuitry as claimed in claim 4 or in claim 4 wherein the parameter is velocity.
7. 7. An instrument and electrical circuitry as claimed in claim 3 or in claim 4 wherein the parameter is distance travelled.
8. 8. An instrument and electrical circuitry as claimed in any one of claims 3 to 7 including an indicator for displaying the parameter.
9. 9. An instrument and electrical circuitry as rerein described with reference to the drawings filed with the Provisional Specification.
10. 10. A vehicle including an instrument and electrical circuitry as claimed in any one of claims 3 to 9.
11. 11. A vehicle as claimed in claim 10 wherein the instrument is installed so that when the vehicle is in motion acceleration forces act in a direction normal to the null position of the lever and in the plane of rotation of the lever.