GB2196114A - Position sensing - Google Patents

Abstract

In a method of detecting the position of an object A, a beam 13 of electromagnetic radiation is rotated about an axis 11 spaced from the beam and two interruptions of the beam by the object are detected; the position can be derived from the corresponding angles of rotation 15, 16 from a datum Y. The position can be displayed. In one form, apparatus has a radiation, e.g. light, source and detector carried on a bar having a shaft which is rotated and a rotary encoder enables the angle of rotation to be derived and the position of the object is derived from the angles at which the beam is interrupted, for example by comparison with data in a computer memory. Use in scoring darts, in signature recognition, in determining the three- dimensional shape of an article, in a keyboard, and in a level (tilt) sensing apparatus are mentioned. Other uses are mentioned. <IMAGE>

Description

SPECIFICATION Position sensing This invention relates to position sensing.

According to this invention a method of sensing position comprises providing a beam of electromagnetic radiation, rotating the beam about an axis at right angles to the beam, the axis being spaced from the beam, and detecting interruption of the beam by an object.

The method may include deriving an indication of the position of the object from the detected interruption.

The method may comprise providing a source of electromagnetic radiation and a detector therefor, rotating the source and detector about an axis spaced from a line between the source and the detector, and detecting the angles of rotation at which the radiation is interrupted.

The method may include deriving from the angles an indication of the position of the object.

The method may include increasing the distance between the beam and the axis. The increase may be continuous or step by step.

The method may comprise effecting relative movement along the axis between the object and the beam.

The method may be used in providing an indication of a score at darts or in signature recognition.

According to another aspect of the invention apparatus for sensing position comprises means for providing a beam of electromag- netic radiation, means for rotating the beam about an axis at right angles to the beam, the axis being spaced from the beam, and means for detecting interruption of the beam by an object.

There may be means for deriving an indication of the position of the object from the detected interruption.

One apparatus has a source of radiation and a detector therefor, and means for rotating the source and detector around the axis, and means for detecting the angles of rotation at which the beam is interrupted.

Another apparatus comprises rotatable radiation-transmitting means having spaced portions between which the beam passes, and stationary means for supplying radiation to said radiation-transmitting means, and means for detecting the angles of rotation at which the beam is interrupted.

The radiation-transmitting means may comprise fibre optics.

The apparatus may include means for deriving from the angles an indication of the position of the object.

The apparatus may include means for increasing the distance between the beam and the axis.

There may be means for effecting relative movement along the axis between the object and the beam.

The apparatus may for example be associated with a dart board, or signature recognition apparatus. Other uses are possible.

The object could be a point and is such as to cause a detectable interruption in the beam.

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described by way of example with reference to the accompanying schematic drawings, in which: Figure 1 is a plan view of a plotting system; Figure 2 is a plan of a plotter; Figure 3 is a side view of Fig. 2 on an enlarged scale; Figure 4 is an electrical circuit; Figure 5 is part of another circuit; Figure 6 is a plan of another plot; Figure 7 is a side view of part of another embodiment; Figure 8 is an enlarged view of part of Fig.

7; and Figure 9 is a side view of the embodiment.

Referring to Fig. 1, in the present system an area 10 which it is desired to plot, that is it is desired to locate the presence of an item on the area 10, has a centre 11 and a periphery 12. A straight plot line 13 in the form of a chord which extends close to the centre 11 is rotated around the centre 11. Considering a point A of coordinates z,B where T is the radial distance between the point A and the centre 11 and 6 is the angle between a datum radius 14 and a line 14a from the centre 11 to the point A, the plot line 13 intersects the point A when the plot line 13 has rotated an angle 15 from the radius 14 and again when the plot line 13 has rotated an angle 16 from the radius 14. By detecting the angles 15, 16 a unique plot of point A can be obtained.The position of point A can be expressed in X, Y coordinates if desired.

All points in the area 10 can thus be plotted, except within the circular area 17 around the centre. The area 17 has a radius equal to the minimum distance between the centre 11 and the chord 13. As the chord 13 rotates, it remains tangential to the circie 17.

Referring to Figs. 2-5, the area 10 is defined on the surface of a body 20 suspending from a mounting 21 and surrounded by a peripheral glass or light-transmitting wall 22. An arm 23 beneath the body 20 extends to both sides of centre 11 and is rotated about the centre 11 by an electric motor 24 through a shaft or rotary encoder 25. The arm 23 is parallel to the plane of the flat surface 10 and at opposite ends respectively carries a source 26 of electromagnetic radiation and a detector 27 for electromagnetic radiation which may be in the visible range but could be outside the visible range e.g. infra-red. The wall 22 could be of perspex.

A stationary pulse transformer 28 supplies energy to a receiving transformer 29, mounted on the arm 23, which energizes the source 26 through a filter 30, also mounted on the arm 23, and conductors- 31, 32. The detector 27 and a further electromagnetic radiation source 33 on the arm 23 at the centre 11 are powered from the filter 30 through conductors 31, 34..Radiation from the source 26 is detected by the detector 27 which energizes the source 33 whose emission is detected by a stationary detector 35.

If an object on the surface 10 interrupts the radiation beam between the source 26 and the detector 27, the source 33 is extinguished whilst this beam is interrupted and this is sensed by the detector 35.

The radiation beam between the source 26 and the detector 27 extends along the chord 13 as seen in plan.

As arm 23 rotates from the datum radius 14, the encoder 25 provides an indication of the angle of rotation, for example by emitting a pulse every degree of rotation or less, and when angle 15 is reached, a pulse is obtained from detector 35. When angle 16 is reached another pulse is obtained from detector 35.

The pulses from detector 35 for example cause signals giving information of angles 15 and 16 to pass to a memory or store of a computer which compares the angles 15, 16 with information in the store to give an indication of the coordinates of point A, which information may be displayed or printed for example. The information may in some circumstances be derived mathematically or obtained by measurement.

The arm 23 may for example rotate at over 500 times a second so that the whole area 10 is scanned at a frequency equal to the frequency of rotation of arm 23.

It will be understood that the Point A need not be stationary and if it is moving a plot can be obtained of its movement.

The area 17 is normally insignificant, e.g. 1 square mm, but it can be scanned if the area 10 (or the motor and arm 23) is moved sideways to a position in which the area 17 is outside the area 17 corresponding to the new centre of rotation of arm 23.

Fig. 5 shows power source 40, box 41 indicating the arrangement of Fig. 3.

In order to plot the periphery of an area 50 Fig. 6, the radiation beam is rotated and, in one rotation, the area 50 causes an interruption in the beam over angular distances 51, between- angular points 52, 53, and 54, between angular points 55, 56. These distance readings can be compared with data in the computer memory to give the angular positions of the points 52, 53, 55, 56 on the periphery of the area 50.If the beam is now moved radially outwardly, say 1 unit, i.e. the radius of area 17 is increased by 1 unit, and a further rotary scan is made, the angular distances and points will change dependent on the periphery of area 50 (examples are shown dotted) and by repeating this at unit radial intervals until the radius of area 17 just equals the maximum distance from the centre 11 to the periphery of the area 50, an indication of the periphery of the area 50 can be obtained for many shapes. In a modification the radius of area 17 is increased continuously.

The area 10 may be notional e.g. the area 50 could be the area of a horizontal section through an article resting on a support, and in this case if the article is moved axially step by step relative to the rotating beam in a direction at right angles to the plane of rotation of the beam, and one or more rotary scans of the beam as required effected at each axial step, a three dimensional indication of the article can be obtained, with suitable correlation between the rotary and the axial movement.

Instead of step by step movement, the movement could be continuous.

The beam can be moved outwardly as above by, for example, mounting the arm 23 on a radial slide with a flexible drive from the motor; or attaching weights to the source 26 and detector 27 which have a radial slide connection with the arm so that as the motor is speeded up the weights are moved outwards by centrifugal force causing the beam to be displaced further from the centre 11.

The device has various uses.

For example, the device may be used in signature analysis. In this case the area 10 receives a signature using a pen. The device, as the pen moves over area 10 during writing of the signature, detects the location of the pen at each scan and compares the sequence of locations (e.g. at over 500 scans or rotations per second) with the sequences of locations corresponding to signatures in the computer memory and gives an indication e.g. visible or audible of whether the signature corresponds to a signature in the store.

If the area 10 is marked to simulate a keyboard, a user's finger can be placed successively on a sequence of simulated keys, the successive positions of the finger detected, and the computer would give an output signal corresponding to the sequence of keys e.g.

for controlling a lock. Such a keyboard would be less liable to damage than one having mechanical or electrical parts. The bed 10 could be sealed so that the keyboard is resistant to water, acids or other chemicals. The area 10 and keyboard can have configurations not normally practical.

One use could be as part of robotic assembly, in which the position of an article being located by a robot is checked by the scanning device and compared with information in the memory to give a servo control to the robot.

The device can be used as part of an automatic scoring device in darts. The dart board forms part of area 10 and the radiation beam is located just spaced above the wires on the dart board. By moving a probe along the wires defining each area of the board the locations corresponding to the peripheries of each area can be placed in the computer memory so that during a game, in which the board is continuously scanned, the area in which a dart lies is detected and allocated by comparison with the store. The areas in the store have associated with them the appropriate score and the computer output can be linked to a visual or other display to give the score for each dart, for each sequence of darts in a throw and running total of points scored, or still to score to reach zero from a start number or to reach a target number from a zero start.

Other uses are possible.

For example the rotating sensor can be associated with an opening, e.g. a door, with the plane of the rotating beam in the plane of the opening, and thus a breach of the opening can be detected and if necessary or desirable connected to operate an alarm, or a recorder to obtain a total of the breaches. The device can simply define a plane and plot and record and breaches of the plane.

In a further embodiment the rotating sensor can be used in a level apparatus with the features of being able to sense and measure to a finite accuracy any deflection in 360" including angle deflection.

The construction is as follows-a framework 50 is constructed around a container 51 which may contain oil or some other means to damp the movement of an arm 52 swinging on a pivot 53 with a weight 54 at the other end. Set below this assembly is a rotating arm 55 with the light source 56, beam 57 and receiver or sensor 58 offset from arm 52 when framework 50 is level on all planes.

As motor 59 revolves thus rotating arm 55, a grid of light beam is created around arm 52.

If framework 50 is now tipped to an angle from level, arm 52 pivoting at 53 will detect the angle by trying to stay central because of weight 54.

The deflection will move the arm 52 off the grid dead area (17) created by the rotating light and break the light beam at a defined point indicating the angle of deflection.

Contained within box 59, as shown in Fig. 7 a frame 60 has fitted a ball race 61 through which is fitted the device shaft 62 of arm 55 and which supports the arm, the shaft carrying a pulley wheel 63. Electric motor 64 has an output shaft 65 carrying a pulley 66 with a belt drive 67 coupled between pulley 66 and pulley 63. When motor 64 runs the arm 55 rotates.

Light source 70 is a set of leds emittors positioned around arm shaft 62 in order to give even light.

This light travels up arm 55 as shown in Fig. 8 through fibre optic material through to emitter point 56. The light passes to receiver 58 and passes back down a fibre optic to receiver 71 in the form of a continuous light or a pulse or period of no light if the beam is broken. Thus in this case there are no electrical connections to the arm 55, the light is transmitted through the arm by fibre optics, or a system of mirrors could be used. This could be applied to the other arrangements. The container and oil are radiation-permeable.

It will be understood that the light beam 13, 57 need not be continuous but could be pulsed, with the timing of the pulses being coordinated with the rate and thus the angle of rotating and the information in the store being derived accordingly.

Claims (27)

1. A method of sensing position comprising providing a beam of electromagnetic radiation, rotating the beam about an axis at right angles to the beam, the axis being spaced from the beam, and detecting interruption of the beam by an object.

2. A method as claimed in Claim 1, comprising deriving an indication of the position of the object from the detected interruption.

3. A method as claimed in Claim 1 or Claim 2, comprising providing a source of electromagnetic radiation and a detector therefor, rotating the source and detector about an axis spaced from a line between the source and the detector, and detecting the angles of rotation at which the radiation is interrupted.

4. A method as claimed in Claim 3, including deriving from the angles an indication of the position of the object.

5. A method as claimed in any preceding claim, including increasing the distance between the beam and the axis.

6. A method as claimed in Claim 5, in which the distance is increased step by step.

7. A method as claimed in Claim 5, in which the distance is increased continuously.

8. A method as claimed in any preceding claim, comprising effecting relative movement along the axis between the object and the beam.

9. A method of sensing position substantially as hereinbefore described.

10. A method of darts scoring using a method as claimed in any preceding claim.

11. A method of signature recognition using a method as claimed in any of Claims 1 to 9,

12. Apparatus for sensing position comprising means for providing a beam of electromagnetic radiation, means for rotating the beam about an axis at right angles to the beam, the axis being spaced from the beam, and means for detecting interruption of the beam by an object.

13. Apparatus as claimed in Claim 12, including means for deriving an indication of the position of the object from the detected inter ruption.

14. Apparatus as claimed in Claim 12 or Claim 13, comprising a source of radiation and a detector therefor, and means for rotating the source and detector around the axis, and means for detecting the angles of rotation at which the beam is interrupted.

15. Apparatus as claimed in Claim 12 or Claim 13, comprising rotatable radiationtransmitting means having spaced portions between which the beam passes, and stationary means for supplying radiation to said radiation-transmitting means, and means for detecting the angles of rotation at which the beam is interrupted.

16. Apparatus as claimed in Claim 15, in which the radiation-transmitting means comprises fibre optics.

17. Apparatus as claimed in Claim 14 or Claim 15 or Claim 16, including means for deriving from the angles an indication of the position of the object.

18. Apparatus as claimed in any of Claims 12 to 17, including means for increasing the distance between the beam and the axis.

19. Apparatus as claimed in Claim 18, in which the distance is increased step by step.

20. Apparatus as claimed in Claim 18, in which the distance is increased continuously.

21. Apparatus as claimed in any of Claims 12 to 20, comprising means for effecting relative movement along the axis between the object and the beam.

22. Apparatus for sensing positionsub- stantially as hereinbefore described with reference to and as shown in Figs. 1 to 6, or Figs. 7 to 9, of the accompanying drawings.

23. Apparatus for using in scoring a game of darts comprising apparatus as claimed in any of Claims 12 to 22.

24. Signature recognition apparatus comprising apparatus as claimed in any of Claims 12 to 22.

25. A method of sensing position however defined.

26. Apparatus for sensing position however defined.

27. Apparatus as claimed in any of claims 12 to 22 associated with a movable structure for detecting movement of the structure.