WO2001052722A1

WO2001052722A1 - Device and method for scanning a beam of light over an object

Info

Publication number: WO2001052722A1
Application number: PCT/SE2001/000059
Authority: WO
Inventors: Martin Krantz
Original assignee: Smarteye Ab
Priority date: 2000-01-20
Filing date: 2001-01-15
Publication date: 2001-07-26
Also published as: SE0000172L; SE515639C2; AU2001228963A1; SE0000172D0

Abstract

The invention concerns a device for detection of a user's direction of gaze, comprising a source of light (1), which is arranged to generate a beam of light (3) in the direction towards the user's eyes (5), and a detector (8) for detection of said beam after reflection thereof towards the eye (5). The device further comprises at least one diffractive disc (20), which is arranged for rotation in a plane extending transversely to the beam of light. The disc (20) is divided into several sectors, each one of which is arranged to deflect the beam in at least one predetermined direction, so that when the disc (20) is made to rotate the sectors one by one pass past the beam of light (3), which is thus deflected in different directions and scan the eyes (5). The invention further comprises a method of utilising the device, and a system for controlling a machine, such as a computer, by means of detection of the direction of gaze of the eyes.

Description

DEVICE AND METHOD FOR SCANNING A BEAM OF LIGHT OVER AN

OBJECT

Technical Field

The present invention relates to a device for scanning a beam of light over particularly an eye, said device comprising a source of light arranged to generate a beam of light in the direction of at least one of the user's eye.

The invention likewise concerns a method of scanning a beam of light over particularly an eye, and a system of controlling for instance a computer by means of eye movements .

Background of the Art With increasing use of computers in most situations, there is an increasing need for control of a computer without exposing the user's body to too heavy stress in the form of load and monotonous movements. It is therefore desirable to control the computer and other equipment by means of eye movements.

Hitherto, the majority of the efforts within this field have been aimed at research or at providing aids for motor-handicapped persons, and in these cases performance in relation to price has not been of primary concern. Consequently, most products developed for these purposes are complicated, ergonomically unsatisfactory and are not cost-efficient.

One category of prior-art solutions, disclosed e.g. in US 4 973 149, comprises a source of light, which illuminates the eye, and a camera based on the CCD or the

CID technology, to read the reflected light. In this manner, an image of the eye is created, which can be analysed and data-processed to generate a signal that may be used to control the computer.

However, a CCD camera or equivalent equipment is limited as to its performance and in addition, it is comparatively expensive. For this reason, this type of solution is unsuitable for use on the consumer market generally.

In accordance with another type of solution, a beam of light is scanned over the eye and is then detected by a detector. One example of this type of system is shown in EP 0 821 908, wherein a divergent laser beam is scanned by means of an SLM (Spatial Light Modulator) over the eye, and is reflected and detected by a PSD (Positive Sensor Detector) . The system disclosed in EP 0 821 908 does, however include several comparatively expensive components, and depends on precise and complex control operations.

In summary, the prior-art devices available on the market are sensitive to misalignment and error- calibration, and they are not intended for mass production. The level of complexity of conventional products therefore makes them unsuitable as mass-produced standard products.

Object of the Invention

The first object of the present invention thus is to provide a device of the kind outlined in the introduction, which in a satisfactory manner combines high-level performance with a low price. Another object of the invention is to provide a device utilising active registration of the eye.

A third object of the invention is to provide a device capable of scanning a beam of light over an eye with a high degree of accuracy, without necessitating too narrow tolerances with regard to manufacture and installation.

A fourth object of the invention is to provide a device that lends itself more readily to mass-production.

Summary of the Invention

These objects are achieved in accordance with the teachings of the invention by means of a device of the kind defined in the preamble, which device is characterised by the provision of at least one diffractive element in the form of a disc arranged to rotate in a plane extending transversely to the beam of light, said disc being divided into several fields, each one of which is arranged to deflect the beam in at least one predetermined direction, whereby upon rotation of the disc the fields pass one by one past the beam of light, thus deflecting the beam in different directions in order to produce scanning of the object or of the eye.

Scanning thus is achieved by refracting the beam of light in the disc, which is allowed one degree of freedom only, viz. rotational movement about an axis. This means that the drive and control needs are minimised, and consequently the device may be configured as a comparatively compact and simple unit. In addition, diffractive optical elements (DOE) in the form of discs are very inexpensive to manufacture. The result is that the price of the device may be kept low without lowering the requirements on performance. At the same time, calibration of the device becomes easier owing to the single degree of freedom of the diffractive element . Not even the precise point of impact of the beam of light on the individual field is a critical aspect, since the entire field deflects the light in the same direction. Comparatively large tolerances therefore are allowable as regards the alignment of each disc, since only one condition need be met, viz. that the beam of light passes through each field.

The beam is generated towards both eyes of the user, which normally is an advantage for determining the direction of gaze.

Each field may be arranged to split the beam of light and to deflect it in several directions. In this manner, a larger amount of data is gathered (more reflections in the eye) upon passage of each field through the beam of light. Fewer fields thus are required for each scan of the eye. The source of light preferably is arranged to generate pulsed light. The disc or the discs then rotate at such a speed that each pulse passes through one field on each disc. Pulsed light eliminates the troublesome refraction phenomena otherwise occurring upon transitions from one field to the next.

According to one embodiment of the invention, the device comprises one first and one second disc each arranged in its respective one of planes that extend normal to the beam of light, the first disc being arranged to deflect the beam of light in a first plane and the second disc arranged to deflect the beam of light in a second plane, which is orientated transversely relative to the first plane. For example, the light is deflected first in an X- axis direction and thereafter in an Y-axis direction.

Although this arrangement requires two discs, it has the advantage of making it possible to manufacture each disc to a comparatively simple pattern.

Alternatively, only one disc is used, which in this case must be configured with fields refracting the light in several planes so as to produce satisfactory scanning.

The fields .are preferably designed as sectors of an annular area of each disc. In addition, a disc may comprise several annular areas, each being divided into several fields . By designing the various fields in the areas differently, the scanning characteristics may be altered by moving the beam of light laterally and allowing the beam of light to pass through different areas. Several beams of light may also be used, which beams in this case pass through different areas of a common disc in order to produce two simultaneous scans having different characteristics. Another aspect of the invention concerns a method of utilising a device in accordance with the invention to scan a beam of light over an object.

A third aspect of the invention concerns a system of enabling a user to give instructions by means of his eyes to for example a computer, comprising means for registering the position of the eye and for generating an electric signal containing data on that position, and means for data processing said signal, to convert the signal into instructions to the computer. In this case, the registering means consists of a device in accordance with the invention, with all the advantages presented above . Brief Description of the Drawing's

The present invention will be described in more detail in the following with reference to the accompanying drawings, which for exemplifying purposes illustrate preferred embodiments of the invention.

Fig 1 is a schematic view of a device in accordance with a first embodiment of the invention.

Fig 2 shows a disc of the device of Fig 1.

Fig 3 shows a device in accordance with a second embodiment of the invention.

Figs 4a and 4b show discs of the device of Fig 3.

Figs 5a and 5b show alternative embodiments of a diffractive disc.

Fig 6 shows a system for control of a computer system by means of the eye, in accordance with one embodiment of the invention.

Detailed Description of Preferred Embodiments

In accordance with the set-up illustrated in Fig 1, a source of light 1, preferably a pulsed IR laser or a

LED, is arranged to emit a beam of light 3 directed towards the face of the user, more precisely towards his/her eyes 5. A system of lenses, in accordance with the shown example consisting of two lenses 7a, 7b, is arranged to focus the beam on the user's face, or more precisely on the plane comprising the user's eyes 5. Having been reflected from the eyes 5, the beam of light 3 is detected by a detector 8, such as a photodiode, for example a PIN diode. One 7a of the lenses is displaceable towards and away from the eyes in order to focus the beam of light 3 on the plane of the eyes. For this purpose, a power means 9 is arranged to move the lens 7a in response to a control signal received from an auto-focusing unit 11 serving to adjust the position of the lens 7a in accordance with the strength of the reflected light received by the photodiode 8. Focusing of this kind is known per se and will not be described in closer detail herein.

One or more diffractive optical elements (DOE) , also known as kinoforms, in the form of preferably essentially circular discs 10a, 10b are located between the lenses. Diffractive discs of this kind may be made for example from a polymer of a suitable kind, which is given the desired shape in a pressing operation, the surface structure being determined by a mathematical description of the desired refraction. The discs 10a, 10b are located in planes extending transversely to the beam of light 3, i.e. planes orientated crosswise to the beam of light, and the discs are arranged to allow passage-through of the beam of light. Preferably, the discs are located in accordance with the shown embodiment in a plane that is normal to the beam of light, although this is not necessary.

Each disc, shown most clearly in Fig 2 and identified in that figure by reference number 10, is divided into a plurality of fields 12, each one of which is designed to refract light passing through the disc, thus deflecting it in a predetermined direction. The various fields are designed to deflect the light to various degrees, and possibly in different directions, in consequence of which the beam of light will scan over the eyes upon rotation of the disc. This process will be described in more detail in the following.

In addition, each disc 10a, 10b is mounted on a shaft 13a, 13b, and a drive unit 15, such as a step motor, is connected to one of the shafts and arranged to cause the discs to rotate. A control unit 17, for instance an intermediate gear-transmission unit, is arranged to ensure a correct gear ratio between the rotational speeds of the discs. Instead of a gear- transmission unit it may of course be quite possible to use a step motor to rotate the discs, and if the discs are to rotate at the same rotational speed, there is no need for a gear-transmission unit. In the boundary layers between the various fields, a minor part of the light may pass through a disc without being deflected. It may therefore be appropriate to arrange for the entire scanning operation to take place upon occurrence of deflection of a predetermined minimum magnitude, and to provide behind the discs a mask allowing passage-through of only slightly deflected light. This technology is known from other technical applications .

In accordance with the embodiment shown in Fig 1, two discs thus are located between the source of light and the eye, the first disc being adapted for refraction of the beam of light in a first direction (for example an X-axis direction) and the second disc being adapted for refraction of the beam of light in a second direction (for example a Y-axis direction) .

As shown in Fig 2, the discs 10a, 10b could comprise an annular area, which is divided into eight circular sectors 12. All sectors 12 refract light in the same plane but at different refraction angles. For example, one of the discs refracts light radially relative to the disc whereas the second disc refracts light tangentially relative to the disc. These directions are constant in each fixed point in space, when the disc is rotating. In addition, each sector 12a is designed to refract light to a higher degree than the preceding, neighbouring sector 12b, whereby the entire scanning interval, i.e. the angular interval to be scanned by the beam of light in one direction may be scanned by rotation of disc 10a,

10b. Various ratios may exist between the number of fields per scanning interval and the total number of fields. In some applications, a ratio of one may be suitable, i.e. all fields refract light in one direction each, and the disc must be rotated over a full turn in order for a complete scan of the direction in question to be effected. In case of limitations of the rotational speed of the discs, the ratio could be a higher integer. A typical scanning resolution, i.e. the number of points that the beam of light is made to hit as a consequence of its refraction, is 320 by 320. Each scanning interval (in the X- and Y-axes directions) therefore requires 320 sector fields. In the simplest fashion, this is achieved by dividing each discs 10a, 10b into 320 fields, but in order to reduce the required rotational speed it could likewise be achieved by using a multiple of 320 fields per disc, such as 640 or 960.

Another embodiment of the invention is shown in Fig 3, in which components that essentially are identical with those in Fig 1 have received the same reference numbers. In accordance with this embodiment, only one diffractive element 20 is provided between the source of light and the eye. In this case, the disc is designed with one field for each intended direction of deflection, such that upon disc rotation the light is refracted in one direction at a time to scan the eye. This arrangement facilitates the control by mechanical means, since only one disc 20 need to be rotated. Fig 4a shows one example of a disc 20, which is designed for use together with the device of Fig 3.

Although in principle, this disc is similar to disc 10a,

10b of Fig 2, the disc 20 must in this case be formed with one field 22 for each refraction angle, which in the present example means 64 fields 22 (see Fig 4) instead of two discs, each having eight fields (see Fig 2) . Each one of the 64 fields produces refraction corresponding to the refraction that the two discs 10a, 10b of Fig 1 produce in combination in a particular position.

In accordance with the above example giving a refraction of 320x320 points, this would means a disc having 320x320=102400 fields. In the case of high degrees of resolution, the manufacture of this type of disc therefore may be complex.

Another embodiment of the disc 20 in the device of Fig 3 is shown in Fig 4b, and it is designated by reference 20'. This disc has only 16 fields 22' but on the other hand, each field is arranged to split the beam of light into several, for instance eight, beams, which are refracted in different directions in such a manner that a bundle of light comprising eight beams hits the eyes and is reflected. In this case, the first eight fields may be arranged to scan this bundle of beams in one direction whereas the following eight fields scan a differently orientated bundle of beams in another direction.

In the case of a 320x320 point resolution, the disc would need 640 fields. The configuration of the discs in conformity with a mathematically calculated structure means that there are no difficulties involved in arranging for each field to split the beam of light into several beams . In accordance with an alternative embodiment one or several of the discs 10a, 10b, 20. 20' may be divided into several annular parts, each one of which is divided into sectors. Each sector-divided annulus may be configured to refract the light at different angles in order in this manner to obtain different scanning angle intervals in conjunction with unchanged resolution, i.e. to "spread" or "compress" the scanning sequence. Fig 5a shows a disc 30 having two annular portions 32a, 32b, divided into fields 34a, 34b, presenting mutually varying deflection angles. The discrete refraction characteristics are indicated in Fig 5a by means of different hatching patterns. In the same manner, each sector-divided annulus may be designed with a smaller or larger number of fields in order to produce different degrees of resolution, possibly in combination with a change of rotational speed and/or pulse rate. Fig 5b shows a disc 40 having two annular portions 42a, 42b, the inner portion 42a having eight fields 44a whereas the outer portion 42b has 16 fields 44b.

In order to allow alternation between the different annular portions 32a, 32b, 42a, 42b all that is required is to displace the beam of light laterally, a movement that it is normally simple to obtain by means of e.g. a lens, or to displace the source of light itself.

Obviously, several beams of light could be used or deflection of a first beam of light into several beams, to make possible simultaneous utilisation of several annuli . It is worth noting that although the above description essentially refers to rectilinear scanning and to rectilinear beam bundles, such references should not be regarded as a restriction of the invention. On the contrary, the scanning directions as also the geometry of these beam bundles are entirely arbitrary. For example, it is quite possible to effect scanning in circular patterns having alternating radii, or according to an arbitrary pattern. Since the design of the fields in the diffractive elements takes place automatically in conformity with a mathematically calculated structure, all scanning geometries that may be defined mathematically are possible. The above-described device is advantageously utilised in a system for control of e.g. a computer by means of eye movements, for example of the kind that is shown in Fig 6.

The system 50 comprises a machine or equipment 52 to be controlled by a user. If it is a computer, the function of the system is identical to that of a conventional mouse. In this case, eye movements thus replace hand movements .

The eye movements are registered with the aid of a device 54 in accordance with the invention, for example of the kind described above. An analogue output signal 56 emitted by the detector 8 is digitalised in an AD converter 62, and the digital signal 64 is then processed in a microprocessor 66 , for example in accordance with a suitable filtering algorithm. This algorithm primarily depends on the type of control that the system is designed to perform, and it may be designed in any suitable manner by an expert in the field. If the control replaces a conventional computer mouse, a calculation is made to determine which cursor-position on the screen corresponds to the position of the eye. Finally, the calculated signal 68 is supplied to the machine 52, which utilises the signal to control a process, a program or the like.

In accordance with one embodiment of the invention, wide-angle scanning may be used to determine roughly the position in space of the user's head, whereafter narrower scanning may be utilised during the control operation proper. If the user moves his head, this may mean that the eyes will leave the scanned area, whereby the wide- angle scanning mode can again be activated. The changes- over from one scanned area to the next can be effected by using a disc comprising several annular portions as described above. The beam of light may then be deflected by means of a lens towards one of the annular portions or else the disc comprising the annular portions may be arranged to be moved laterally.

It is easily understood that the invention as defined in the appended claims is not limited to the embodiments described herein. On the contrary, a plurality of modifications and variations are possible as is readily understood by the expert in the field.

For example, the division of the discs into fields may be varied with respect to the shape of the fields and their number. The dimensions of the discs as also the relative dimensions of the fields in relation to the discs are best determined by the expert in each individual case. The shown discs are to be regarded as examples only and are intended to illustrate a principle, and therefore no precise measurements are given. In addition, other drive means may be utilised in order to control the discs, as also other combinations of lenses and other optical elements may be suitable, depending on the intended application.

Claims

1. A device for scanning a beam of light over an object, particularly an eye of a user, said device comprising a source of light (1) arranged to generate a beam of light (3) in the direction of the object (5) , c h a r a c t e r i s e d in that at least one diffractive element in the form of a disc (10a, 10b; 20) is arranged for rotation in a plane extending transversely to the beam of light, said disc (10a, 10b; 20) being divided into several fields (12; 22), each one of which is arranged to deflect the beam in at least one predetermined direction, whereby upon rotation of the disc (10a, 10b; 20) the fields (12; 22) pass one by one past the beam of light (3), thus deflecting the beam in different directions in order to produce scanning of the object (5) .

2. A device as claimed in claim 1, wherein the beam (3) is generated in a direction towards both eyes (5) of the user.

3. A device as claimed in claim 1 or 2 , wherein each field (12; 22) is arranged to split the beam of light (3) and to deflect it in several directions.

4. A device as claimed in any one of the preceding claims, wherein the source of light (1) is arranged to generated a pulsed light.

5. A device as claimed in any one of the preceding claims, comprising one first and one second disc (10a, 10b) , each arranged in its respective one of planes that extend normal to the beam of light, the first disc (10a) being arranged to deflect the beam of light in a first plane and the second disc (10b) arranged to deflect the beam of light in a second plane, orientated transversely relative to said first plane.

6. A device as claimed in any one of the preceding claims, wherein each field (12; 22) is a sector of said disc.

7. A device as claimed in any one of the preceding claims, wherein at least one disc (30; 40) comprises two annular portions (32a, 32b; 42a, 42b) , each one of which is divided into a plurality of fields (34a, 34b; 44a, 44b) .

8. A device as claimed in any one of claims 2-7, said device further comprising a detector (8) to detect the beam after reflection of said beam from the eye (5) , in order thus to allow detection of the user's direction of gaze.

9. A device as claimed in any one of the preceding claims, said device further comprising a second source of light.

10. A device as claimed in any one of the preceding claims, wherein said detector (8) is a photodiode .

11. A device as claimed in any one of the preceding claims, wherein said source of light (1) is a laser.

12. A device as claimed in any one of the preceding claims, wherein said source of light (1) is a LED.

13. A device as claimed in any one of the preceding claims, wherein the wavelength of said source of light is within the IR range.

14. A system of making it possible for a user to give instructions to a machine (52) , such as a computer, by means of changing the direction of gaze of the eyes, comprising means (54) for registering the direction of gaze of the eyes and for generating an electric signal (56) containing data on said direction of gaze, and means (58, 62, 66 ) for converting said signal into instructions ( 68 ) to the machine , c h a r a c t e r i s e d in that said registering means (54) comprise a source of light (1) arranged to generate a beam of light (3) in the direction towards the eyes (5) , a detector (8) to detect the beam after reflection of said beam from the eyes, and at least one diffractive element in the form of a disc (10a, 10b; 20) , said disc being arranged for rotation in a plane extending transversely to the beam of light (3) and being divided into a plurality of fields (12; 22), each one of which is arranged to deflect the beam in at least one predetermined direction, whereby upon rotation of the disc (10a, 10b; 20) the fields (12; 22) pass one by one past the beam of light (3) , thus deflecting the beam in different directions in order to produce scanning of the eyes (5) .

15. A system as claimed in claim 14, wherein said instructions (68) comprise determination of the position of a cursor on a computer screen.

16. A method of scanning a beam of light over an object, particularly the eyes of a user, comprising the steps of generating a beam of light (3) in a direction towards the object, particularly towards the user's eyes (5) , and of scanning said beam over the object, c h a r a c t e r i s e d in that the step of scanning said beam comprises the steps of bringing the beam to pass through a diffractive element in the form of a disc (10a, 10b; 20) , which is arranged for rotation in a plane extending transversely to the beam of light (3) , said disc being divided into a plurality of fields (12; 22), each one of which is arranged to deflect the beam in at least one predetermined direction, and rotating the disc to ensure that the fields pass one by one past the beam of light (3), thus deflecting said beam in different directions.

17. A method as claimed in claim 16, further comprising the step of detecting the beam after reflection thereof towards the eyes (5) , in order thus to allow detection of the user's direction of gaze.