SPECIFICATIONPosition detector systemThe invention relates to a detection system for indicating the position of an object within a designated area.
There is a need in various situations to determine the presence and the accurate position of an object within the boundaries of a designated area. One such application is in interactive computer systems which employ a transparent touch sensitive membrane which is placed over the screen and by pressing the required portion of the membrane this designates the position of the object (e.g. a finger) within the screen area and produces a desired function from the screen display. However, such membranes are of a soft plastics material which tends to become scuffed or scratched in use causing a degredation in the quality of picture transmitted therethrough.
The present invention is concerned with providing a position detector system which is accurate and does not require physical or mechanical contact with the sensor.
According to the invention there is provided a detection system for indicating the presence and/or position of an object within a designated area, said system comprising a plurality of emission sources adjacent the area boundary each operable to produce a number of divergent signal paths within said area and a plurality of detector means each for detecting the plurality of detector means each for detecting the attenuated emission by the object from each associated source when operable, to produce a detection signal.
The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a basic matrix configuration of transmitters and receivers;Figure 2 shows an enhanced resolution system employing divergent signal paths;Figure 3 shows a simplified location determining arrangement;Figure 4 shows a more complex arrangement;Figure 5 shows the absolute position from means intercept values;Figure 6 shows an arrangement for providing and calculating the above values; andFigure 7 shows an embodiment of the invention in more detail associated with a video screen bezel.
A basic detection matrix is shown in Fig. 1 and comprises a plurality of transmitters and receivers along opposite boundaries of the sensing area. The transmitters may typically comprise infra-red light emitting diodes and the receivers may be photo-sensitive diodes or transistors.
Such LEDS are chosen to ensure a parallel output beam.
These devices may be provided within a framework unrestricted view of the screen. By simply pointing at a desired function using a finger, the operator is in effect choosing the crosspoint between the X and Y transmitters/receivers and this defines the X and Y coordinates which is usable by the system computer in a similar way to a keyboard entry. In the example shown employing 7 X 4 transmitters/receivers there are 28 active crossing points. Where a larger selection capability is required, troubles can arise with regard to resolution. When increasing the number of active crossover points, difficulty in physically realising the system arises. In addition, with an increase in the number of crossings,a finger may break the beams from several transmission paths.
In order to cope with the first of these problems a modified configuration is shown in Fig. 2 which is configured to also be suitable for a variety of detection area uses. Here divergent beams are provided (using inherently divergent LEDS or by incorporating divergent lenses in combination with the LEDS).
The number of crossing points is dramatically increased. In the example shown employing a 7 x 4 matrix the number of active points has increased from 28 to 784 (i.e. 42 x 72). Due to the divergence of the beams however, amplification of the received signal is typically required to compensate, as only a small portion of the original signal reaches any one photoreceiver.
An example of how the system operates is illustrated by the simplified system of Fig. 3.
A transmitter TA is located to provide a divergent beam which is received by receiver arrayRA. In addition a further transmitter TB is located to provide a divergent beam for receipt by receiver array RB. Each array is shown to contain 1 6 elements. In the example shown receiver number 14 in array RA fails to receive light from TA due to the presence of the object and similarly receiver number 1 2 fails to receive light from TB.
As the coordinates of the transmitter origins are known and the detected points are also now known it is possible to calculate the crossover point by using the general equation for a lineY = mx + cIn this case y - y2 = m' (x - x2) (1) and y - y0 = m (x - x0) (2) thus Y1 - Yo m=x1 - x0 andx3 - y2 m' =x3 - x2 and substituting in (1) and (2) we get the equation( y3 - y2 ) y = () (x - x2) + y2 (3)( x3 - x2 ) and( y1 - y0 ) y = () (x - x2) + y0 (4)( x1 - x0 )Using the transmitter and receiver configuration shown x0 = 0X1 = 15 y2 = 0 y3 = 15From 3( 15 - 0 ) y = () (x-x2) + 0( x3 - x2 )15= (x-x2) (5)x3 - x2 and from 4( y1 - y0 )Y = () (x - 0) + y0( 15 - 0 )( y1 - y0 ) y = () x + y0 (6)15By substitution15y0 (x3 - x2) + 225 x2x = (7)225 - (y1 - y0) (x3 - x2)Thus by calculating x from (7) it is possible to then insert this value in (5) to give y.
In the example xO= O; yO=O; x, = 15; y1 = 14 x2 = 12; y2 = 0; X3= 0; y3 = 15Thus225 x 12 x =225 - (14 x - 12)225X 12= = 6.87225+(14X 12) and14 X 6.87 =6.41 15Thus the coordinates of the object position are now available.
In practice the object will typically interrupt more than one light path as shown in Fig. 4. Here the absence of a beam is indicative of a logic 1 state. The mean is calculated by an averaging technique.
Thus13+14+15 y'r = = 143 and 10+11 + 12+13+14 y'r = = 125 as in the simple case above.
Where a number of transmitters are provided along the sensing periphery then averaging of their resultant individual readings will be required thus: 2;n x'n = X2 the averaged intersect coordinate on the xr axis.
En xt = X3 the averaged intersect coordinate on the x' axis.
#n y/r = y, the averaged intersect coordinate on the y, axis.
#n y, = y0 the averaged intersect coordinate on the y, axis.
where n = number of active response cycles.
This will tend to give a shift in the origins of the beams as shown in Fig. 5. Thus the values of y0 and x3 for example are no longer zero. Nevertheless the computation will result in the same values for coordinates x, y as above.
In practice all the values for each detected attenuation from the series of transmitter excitations through the scan may be accumulated and the averaged or mean value calculated from the accumulated value.
A typical arrangement for handling the data generation and computation is shown in Fig. 6.
A RAM 20 receives data from the receiver arrays under control of input address generator 21 which also addresses the transmitters to provide the active response cycles. The stored data is made available from the RAM by processing under the control of output address generator 24.
The data is also received by a first calculate 22 which computes the mean x and y values. These values are then used by second calculator 23 to provide the absolute or cross-over value.
Although processors 22 and 23 can be formed from standard hardware blocks (e.g. adders, subtractors and multipliers) in practice it is convenient to employ microprocessor techniques to effect the computation by changing the internal functions under firmware control (using a EPROM for example).
In a specific application shown in Fig.7, the detector configuration is employed fordetermining the position of a finger placed within a video display unit screen area (e.g. cathoderay or plasma arc screen).The rear view of bezel 30 is shown and is configured to fit on theperiphery of the display screen; the inner wall 30a abutting the screen and the outer wall 30bbeing flush with the unit housing. The well area therebetween is sufficient to house the circuit components. A number of horizontally mounted infrared LEDS 31 are provided with a similarnumber of receivers 32. A number of vertically mounted LEDS 33 are provided opposite a similar number of receivers 34.The emitters typically have a beam spread angle of about 60 so, as shown, the outer emitters are mounted to point towards the centre of the receivers to ensure receipt by them all, as this is preferable to only some receiving the emitted signals. The output of each receiver 32 is typically amplified by an associated amplifier 35 (only one is shown) and may also operate as a threshold device to provide binary logic status dependent on interruption or severe attenuation. The output from each of the amplifiers may be multiplexed via multiplexer 36 to reduce the number of wires required to be provided at the output. A similar configuration is employed for the other set of receivers. Each emitter can be sequentially excited (multiplexed as necessary) and the status of all receivers determined at each stage.
The data outputs can be received as binary signals without further modification by RAM 20 ofFig. 6 for example. Suitable plastics material (e.g. ICI 962)) is chosen for bezel 30, which is opaque to visible light but non-opaque to infra-red, so that no visible apertures are required to detract from the presentation of the housing. The x and y co-ordinate values can be used by the micro computer associated with the display in a similar way to switch actuation information.
With a 14" (diagonal) screen, which gives about 12" horizontally, the number of emitters could be 26 horizontally, and 20 vertically, with similar number of receivers. If these were to be non divergent the resolution would be only 1 2/26-0.5".
With the divergent configuration employed the resolution increases so that each emitter effectively has 26 beams as this is the number of detectors which receive the output from any one emitter, so that the resolution is 26 times better. The resolution is now of the order of 0.02". The very high resolution is of such a system makes it applicable to other areas of use. A slight inrease in density of emitters (e.g. every 1 /4" or 1 /8") makes the resolution within the detection area sufficiently accurate to be of use in machine tool detection or positioning.
A reduction in density (e.g. every 30") will allow low cost coverage of large detection area (e.g. bank vaults) without the possibility of avoiding the beam detector. Majority logic gating can be employed to avoid false alarms by small objects (e.g. mice). The system can be employed in external security areas or around windows or doors to detect intruders before entrance is gained.
With additional processing it is possible to calculate the size of objects detected within the area, as their position and the number of beams attenuated is made available.
As a result of effectively incrementing the detection process around the perimeter of the area, it is possible to determine the external shape or outline of an object and reconstruct it's image on a printer of visual display device, or alternatively, electronically compare the outline or shape with a reference shape held in a computer or obtained from a television camera.
Although the selection application described has been for dynamic information provided by a display terminal, the selection could be associated with display areas of static or permanent form, such as graphs, drawings, flowcharts or other visually presentable information. Alternatively the area could be a panel with a number of switch patterns displayed allowing remote actuation.
Whilst the system has generally been described as determining the presence for an object, it would be applicable to detecting the removal of an object from a predetermined position following its presence.