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Interrupted reflection fibre optic communication device for the severely disabled
INTERRUPTED REFLECTION FIBRE OPTIC COMMUNICATION DEVICE FOR THE SEVERELY DISABLED K.T.V. Grattan
and A.W.
Palmer
ABSTRACT llu dz@erence between light refitted jkom the open qe and that reflected firn the closed lid is d&&d by means of an opticjbre attached to a spectacle frame. That dt@rerwe is processed electronically to produce a
Keywords: aids for the disabled, communication,
fibre optics, sensors, spectacles, infra-red optics.
INTRODUCTION The use of fibre optics in sensor systems is one of the more interesting developments which has arisen from telecommunications technology. Fibre optics now represent a substantial market in their own right with, amongst others, applications in measurement and control in medicine’. The rapidly decreasing cost of the fibres themselves and also of the electronic devices employed to process their signals, heralds a much wider application in future years. An inexpensive fibre optic communication device has been constructed, with the aim of enabling certain classes of severely disabled eople to communicate, in any of a variety o P ways, with the outside world. There is for example, a number of patients who in addition to being paraplegic, lack also the ability to speak; one of the few functions still available to them is movement of the eyes and eyelids. This function is used here as the stimulus for a system which detects light reflected from the open eye, primarily from the sclera, and then compares it with light reflected from the closed eyelid - a binary signal. An optical fibre is held unobtrusively in a spectacle frame in front of the eye in a non-critical position, thereby obviating the need for accurate alignment when the s ectacles are removed and replaced. By means o P a relatively simple electronic device, a sufficiently large difference in signal is made available to distinguish between eyelid open and eyelid closed. CONSTRUCTION
pulse train which may be interpreted either subjectively by a ‘listener or physicallyfor the purpose of controlling external devices. Involuntary blinks may be suppressed Potential developments of the techniqw are discussed
located round the spectacle frame, and less brittle than glass (silica) fibre; its higher attenuation is insignificant over the few metres of fibre used. It was originally thought that a second fibre, carrying low power invisible infra red light from a photodiode, would be necessary; or alternatively that the single fibre would be coupled into two separate fibres, one for transmission to the eye and the other for reception of the reflected signal. However, this was found to be unnecessary since adequate signal levels could be obtained in daylight or in an artificially lighted room. Light falling on the eye is scattered, some being picked up by the single fibre, the output of which is modulated by normal eyelid closure. Information is communicated by generating a series of lid closure pulses, whose individual lengths are significantly greater than that of an involuntary blink, approximately 0.1 s; these relatively short pulses, representing blinks, may be filtered from the pulse sequence in the processing electronics. The output from the photodiode is filtered and then displayed on an oscilloscope; it is this display that the ‘listener’ reads. Alternatively the signal may be further processed to display
SPECTACLE
FRAME
4N\
AND OPERATION
optical The optical and mechanical aspects of the device are illustrated in Figure 1. A step-index polymer fibre of core diameter 1.0 mm and overall diameter 2 mm is held close to the eye; it is mounted on an opticians trial frame but conventional spectacles could be used without interfering with normal vision. For this application, polymer fibre is less expensive, more flexible - it may be conveniently Measurement and Instrumentation Centre, School of Electrical Engineering and Applied Physics, The City University, London, EClV OHB, UK.
0 1984 Butterworth & Co (Publishers) Ltd 0141-5425/84/040321~02 SOS.00
FIBRE OPTIC Figure device
1
Diagrammatic
. representation
of the fibre optic
J. Biomed Eng. 1984, Vol. 6, October
321
Fibre-optic device: K. T. 1/ Grattan and A. W Palmer
I -V
CONVERTER
AMPLIFIER
LOW PASS
A-TYPE Figure 2
I
0
Circuit diagram for the electronic
1
1
3
CA3140E
signal processing
I
2
FILTER
4
difference in pulse lengths may readily be distinguished by elementary digital methods, or by observation; variations in ambient light levels will not affect the relative pulse durations. If the user were obliged to be in a dark environment, it would be possible to revert to the original concept of using a low power infra-red (invisible) source connected to a second fibre.
TIME 6) Figure 3 Typical output pulses as observed on an oscilloscope, showing two involuntary and then two voluntary pulses
readable messages or to control external devices which the user otherwise would be unable to control for himself. Electrical The light detector is a planar silicon PIN photodiode (RS 309-307), having a low operating voltage and a fast response. Its spectral characteristics coincide well with the emission of a typical tungsten lamp, the peak response being just outside the red visible region at 850 nm. The photodiode output is led to a current-to-voltage converter, in which a shunt capacitor (56 pF) attenuates high frequency noise; power supply frequency interference and any other ‘low frequency’ noise is attenuated by a second order low pass filter. The overall passband is d.c. to 20 Hz, adequate for the passage of the information bearing pulses. (figure 2). Output characteristics A typical output signal is illustrated in Figure 3, which shows clearly two involuntary blinks followed by two voluntary eye closures. The
322
J. Biomed Eng.
1984, Vol. 6, October
CONCLUSIONS
AND FUTURE DEVELOPMENT
This investigation has demonstrated the principles of a device which the severely disabled could use, without inconvenience, to control a wide range of domestic equipment: lights, radio, television etc. At this stage in its development the output is displayed on an oscilloscope or trace recorder, but with the aid of modern technology there is considerable scope for future development - a suitable eye-closure pulse train could for example be the stimulus to a microprocessor controlled voice synthesiser or message display panel. Projects now being actively pursued are aimed at exploiting the potential of the method, with the object ultimately of entering into commercial production.
ACKNOWLEDGEMENTS The authors wish to thank the Rehabilitation Engineering Movement Advisory Panel for its financial support; and Mr. J.D. Rana for his help in the construction of the electronic equipment.
REFERENCES 1 Grattan, K.T.V. Fibre optic sensors for temperature, pressure and flow measurement. Measurement (Journal of the International Measurement Confederation). In press.
and A.W.
Palmer
ABSTRACT llu dz@erence between light refitted jkom the open qe and that reflected firn the closed lid is d&&d by means of an opticjbre attached to a spectacle frame. That dt@rerwe is processed electronically to produce a
Keywords: aids for the disabled, communication,
fibre optics, sensors, spectacles, infra-red optics.
INTRODUCTION The use of fibre optics in sensor systems is one of the more interesting developments which has arisen from telecommunications technology. Fibre optics now represent a substantial market in their own right with, amongst others, applications in measurement and control in medicine’. The rapidly decreasing cost of the fibres themselves and also of the electronic devices employed to process their signals, heralds a much wider application in future years. An inexpensive fibre optic communication device has been constructed, with the aim of enabling certain classes of severely disabled eople to communicate, in any of a variety o P ways, with the outside world. There is for example, a number of patients who in addition to being paraplegic, lack also the ability to speak; one of the few functions still available to them is movement of the eyes and eyelids. This function is used here as the stimulus for a system which detects light reflected from the open eye, primarily from the sclera, and then compares it with light reflected from the closed eyelid - a binary signal. An optical fibre is held unobtrusively in a spectacle frame in front of the eye in a non-critical position, thereby obviating the need for accurate alignment when the s ectacles are removed and replaced. By means o P a relatively simple electronic device, a sufficiently large difference in signal is made available to distinguish between eyelid open and eyelid closed. CONSTRUCTION
pulse train which may be interpreted either subjectively by a ‘listener or physicallyfor the purpose of controlling external devices. Involuntary blinks may be suppressed Potential developments of the techniqw are discussed
located round the spectacle frame, and less brittle than glass (silica) fibre; its higher attenuation is insignificant over the few metres of fibre used. It was originally thought that a second fibre, carrying low power invisible infra red light from a photodiode, would be necessary; or alternatively that the single fibre would be coupled into two separate fibres, one for transmission to the eye and the other for reception of the reflected signal. However, this was found to be unnecessary since adequate signal levels could be obtained in daylight or in an artificially lighted room. Light falling on the eye is scattered, some being picked up by the single fibre, the output of which is modulated by normal eyelid closure. Information is communicated by generating a series of lid closure pulses, whose individual lengths are significantly greater than that of an involuntary blink, approximately 0.1 s; these relatively short pulses, representing blinks, may be filtered from the pulse sequence in the processing electronics. The output from the photodiode is filtered and then displayed on an oscilloscope; it is this display that the ‘listener’ reads. Alternatively the signal may be further processed to display
SPECTACLE
FRAME
4N\
AND OPERATION
optical The optical and mechanical aspects of the device are illustrated in Figure 1. A step-index polymer fibre of core diameter 1.0 mm and overall diameter 2 mm is held close to the eye; it is mounted on an opticians trial frame but conventional spectacles could be used without interfering with normal vision. For this application, polymer fibre is less expensive, more flexible - it may be conveniently Measurement and Instrumentation Centre, School of Electrical Engineering and Applied Physics, The City University, London, EClV OHB, UK.
0 1984 Butterworth & Co (Publishers) Ltd 0141-5425/84/040321~02 SOS.00
FIBRE OPTIC Figure device
1
Diagrammatic
. representation
of the fibre optic
J. Biomed Eng. 1984, Vol. 6, October
321
Fibre-optic device: K. T. 1/ Grattan and A. W Palmer
I -V
CONVERTER
AMPLIFIER
LOW PASS
A-TYPE Figure 2
I
0
Circuit diagram for the electronic
1
1
3
CA3140E
signal processing
I
2
FILTER
4
difference in pulse lengths may readily be distinguished by elementary digital methods, or by observation; variations in ambient light levels will not affect the relative pulse durations. If the user were obliged to be in a dark environment, it would be possible to revert to the original concept of using a low power infra-red (invisible) source connected to a second fibre.
TIME 6) Figure 3 Typical output pulses as observed on an oscilloscope, showing two involuntary and then two voluntary pulses
readable messages or to control external devices which the user otherwise would be unable to control for himself. Electrical The light detector is a planar silicon PIN photodiode (RS 309-307), having a low operating voltage and a fast response. Its spectral characteristics coincide well with the emission of a typical tungsten lamp, the peak response being just outside the red visible region at 850 nm. The photodiode output is led to a current-to-voltage converter, in which a shunt capacitor (56 pF) attenuates high frequency noise; power supply frequency interference and any other ‘low frequency’ noise is attenuated by a second order low pass filter. The overall passband is d.c. to 20 Hz, adequate for the passage of the information bearing pulses. (figure 2). Output characteristics A typical output signal is illustrated in Figure 3, which shows clearly two involuntary blinks followed by two voluntary eye closures. The
322
J. Biomed Eng.
1984, Vol. 6, October
CONCLUSIONS
AND FUTURE DEVELOPMENT
This investigation has demonstrated the principles of a device which the severely disabled could use, without inconvenience, to control a wide range of domestic equipment: lights, radio, television etc. At this stage in its development the output is displayed on an oscilloscope or trace recorder, but with the aid of modern technology there is considerable scope for future development - a suitable eye-closure pulse train could for example be the stimulus to a microprocessor controlled voice synthesiser or message display panel. Projects now being actively pursued are aimed at exploiting the potential of the method, with the object ultimately of entering into commercial production.
ACKNOWLEDGEMENTS The authors wish to thank the Rehabilitation Engineering Movement Advisory Panel for its financial support; and Mr. J.D. Rana for his help in the construction of the electronic equipment.
REFERENCES 1 Grattan, K.T.V. Fibre optic sensors for temperature, pressure and flow measurement. Measurement (Journal of the International Measurement Confederation). In press.