GB2176282A - Optical position locating device - Google Patents

Abstract

An optical position locating device (10) comprises a frame (12) defining a generally rectilinear target zone (14), a pair of light sources, detectors and structure (24, 26) for directing the light initially from each light source to the target zone (14) and for scanning across the target zone and directing light returned from the target zone (14) to the associated detector. The target zone (14) is substantially rectangular and the two light sources and light detectors with their associated light directing structures (24, 26) are respectively positioned at each of a first and second corner of the target zone (14) along a common first side. A plurality of reflective structures (18, 20, 22) are arranged about the target zone (14) and include first (18) and second (20) reflector assemblies in generally mutually facing relationship to define second and third opposite sides of the target zone (14) and a third reflector assembly (22) defining the fourth side of the target zone (14) which is opposite the first side. Each of the first (18), second (20) and third (22) reflector assemblies comprising retroreflective material. <IMAGE>

Description

SPECIFICATION Optical position locating device The present invention is directed to an improved optical position locating device, and more particularly to a device for determining the location of an object within a target zone by optical means.

While the device of the invention may find utility in a variety of applications, the disclosure will be facilitated hy specific reference to its use as an optical touch screen input device for a computer or computer-like apparatus.

The increasing prevalence of such computers and other computer-like apparatus have given rise to the recognition of a need for simplifying the human operator-to-computer interface, for example to facilitate the input of data to the computer or other apparatus. Such devices as keyboards, joy stick controls, and various types of "touch screen" input apparatus have been devised.

The latter type of touch screen input apparatus are generally utilized with the cathode ray tube type of display element utilized with many computers and computer terminals.

These touch screen input apparatus include screen overlays superimposed upon cathode ray tube display screens, which input apparatus may be of capacitive or resistive type, or alternatively may be ultrasonic or consist of a conductive grid. Generally speaking, the overlays detect and determine the location of a pointer, finger or the like relative to the display screen for selecting or indicating a portion of the displayed information. However, the use of such oVerlays in front of the cathode ray tube display tends to degrade the visual quality of the display as it appears to an operator. That is, such an overlay may degrade not only the contrast and brightness of the display as it appears to the operator, but also may degrade the resolution of the display.In many applications, the increased resolution of the display is an important operating feature, such that the addition of an overlay which degrades resolution is undesirable.

Moreover, such oVerlays may attract and trap dirt, dust, or the like to further contribute to the degradation of the display quality. In this regard, such overlays are often made of materials which may be easily scratched or otherwise further damaged with time or use, further adding to the problems of display visual degradation. These materials may also greatly reduce the effectiveness of non-glare cathode ray tube display area finishes. As an additional matter, such overlay touch screens generally increase in-both complexity and expense of manufacture when increases of resolution in their own detection or position-locating capabilities are effected.

Optical touch screen input apparatus have been proposed to overcome the aforementioned shortcomings of touch screen overlays.

Such optical apparatus generally create a "light curtain" in front of the cathode ray tube or other display, preferably in a non-visible infrared range, so as not to interfer visually with the appearance of the display to the operator.

Penetration of this curtain by an object, such as the finger of an operator, a pencil, or the like is readily detectable by the apparatus and is interpreted to fix the location of penetration of the object relative to the touch screen and hence relative to the display screen.

In one such optical touch screen input apparatus which has had widespread acceptance and is described in EP-A-0125068, a generally rectilinear frame defines a generally rectangular target zone. A light distribution and detection apparatus is mounted at one corner of the frame and directs light into the target zone.

Reflection assemblies extend along either side of the target zone from a corner thereof opposite the corner at which the light distribution and detecting assembly is located. A third reflective assembly is positioned to span a further side of the target zone intermediate the otherwise free outer end of one of the first two assemblies in the corner in which the light distribution and detecting apparatus is located. This third reflective assembly and the reflective assembly which it abuts comprise retroreflective assemblies which are arranged to reflect light incident thereupon directly back along its path of incidence. The remaining reflective assembly preferably comprises a mirror arranged to reflect light emitted from the light source back to one of the retroreflective assemblies, and vice versa.

The detector is located for detecting the light returned from the respective retroreflective assemblies and mirror. A scanning assembly is provided for scanning the target zone for receiving the return beams of light therefrom. Hence, a determination of the angular position of the scanning assembly at any given instant relative to the target zone also determines the angular orientation of the path of the return light incident at that moment upon the detector. The presence of an object in the target zone will cause a marked decrease in the amount of light reflected at at least two angular orientations. The first of these orientations is that at which a beam reaches the object directly from the source and is reflected directly back to the detector by one of the retroreflector assemblies.The second of these angular orientations is that at which the beam of light is reflected from the mirror during one or both of its lines of travel from source, to object, to retroreflector and back again to the detector. Upon determining the two angles at which decreased return light energy is detected, the position of the object relative to the two dimensions of the display screen may readily be determined.

While the foregoing system has found wide spread acceptance, there is room for yet further improvement. For example, in optical systems of this type there is always the problem of light losses encountered in the device, which detract from the net amount of light reaching the detector. To maximize the sensitivity and resolution of the device, it is desirable to maximize the net amount of light energy and hence the contrast between reflected light reaching the detector directly as opposed to light blocked by the object which is to be detected. Hence, loss of available light within the target area of the device may detract from both resolution and sensitivity of the device, and such losses are particularly noticeable as the size of the target zone increases.Also, in the foregoing device, wherein a mirror is uti lized as one of the reflective surfaces, as briefly explained above, it is usually found desirable to utilize a filter in front of the mirror to limit the reflected light to the infrared wavelengths utilized, thus avoiding some of the undesirable effects of ambient light present in the operating environment. This latter problem of susceptibility of such devices or apparatus to the effects of ambient light must also be addressed in such a device. however, it should be appreciated that the use of such additional filters and the like will further contribute to light losses in the device.

Moreover, holding mechanical tolerances in the positioning and assembly of the various parts of the touch screen device becomes more and more critical as the overall size thereof is increased. In this regard, as the size of the mirror portion thereof increases, it becomes more and more difficult to build a substantially flat and uniform mirror within the desired tolerances. it will be appreciated that maintaining the reflective properties of the mirror within desired tolerances is important in that light reflected from the mirror may otherwise fail to reach the retroreflective surfaces, resulting in potential loss of resolution, or even "blind spots" in the device.On the other hand, since retroreflector devices by their nature return the light in the same direction as that of light incident thereupon, the correct positioning and mounting as well as maintaining tolerances during the fabrication thereof are not nearly so critical as with a mirror.

In this regard, such optical position locating devices have been used with display screens of up to on the order of twenty-five inches (625 mm) diagonal measurement without encountering significant losses. However, it is now desired to greatly increase the size of the device, for utilization in connection with a display screen of as large as on the order of ten feet (3 m) in diagonal measurement. It will be appreciated that the problems of light losses in the target area can become particularly acute in devices of such greatly increased size.

According to this invention an optical position locating device comprises a four-sided, rectilinear frame assembly defining a target zone within which the position of an object is to be located by the device; a pair of light distribution and detecting assemblies respectively located at opposite ends of one side of the frame, each of the light distribution and detecting assemblies comprising a light source, detector means for detecting light and producing a corresponding output signal, and light directing means for directing light from the light source to the target zone; the detecting means being positioned for receiving light from the target zone; and retroreflecting means arranged about the target zone for reflecting incident light along a path substantially coincident with the path of incident light; the retroreflecting means comprising three retroreflective members respectively arranged along a side opposite said one side and both of the other pairs of sides of the target zone; and, scanning means operatively associated with the detector means for determining the angular displacement of light received thereby relative to the target zone, so that the presence of an object within the target zone registers upon the detector means as a change in light intensity at a given angular displacement; whereby the location of an object within the target zone is determined in two dimensions from the respective angular displacements of the changes in light intensity incident upon the two detector means.

The present invention provides an optical position locating device which is capable of locating the position of an object in a target zone which is significantly larger than with previous such devices.

A particular example of an optical positionlocating device in accordance with this invention will now be described with reference to the accompanying drawings; in which: Figure 1 is a front elevation, somewhat diagrammatic in form; Figure 2 is a side elevation of part of one form of light distributing and detecting apparatus drawn to a larger scale; and, Figure 3 is a side elevation of part of an alternative form of light distribution and detecting apparatus, again drawn to a larger scale.

Referring now to the drawings, and initially to Figure 1, an optical position locating device in accordance with the invention is designated generally by the reference numeral 10. The device 10 is comprised of a housing or frame assembly 12 which serves to maintain the various elements of the device 10 in proper relation as well as to protect these elements from environmental incursions. The housing or frame assembly 12 is generally rectilinear in configuration and serves to define a rectilinear or rectangular target zone 14 within which target zone 14 the location of objects is to be determined.

The target zone 14 is further defined by a first or top side 16 of the housing and by respective reflector means or assemblies designated generally by reference numerals 18, 20 and 22, located along sides 19, 21 and 23 of the frame 12. The reflector means 18 and 20 are located at and generally define second and third opposite sides of the target zone 14, and the reflector means or assembly 22 is located along and defines generally a fourth side of the target zone 14, generally opposite the first side 16. In accordance with a feature of the invention, each of these reflector means or assemblies 18, 20 and 22 is comprised of a retroreflective material. A retroreflective material will be understood to refer to a material which tends to reflect light incident thereupon substantially directly back along the path of incidence.

In accordance with a further feature of the invention, a pair of similar light distribution and detecting assemblies 24 and 26 are mounted generally adjacent the respective corners 28 and 30 defined at opposite ends of the first or top side 16 of the frame 12. That is, these assemblies 24 and 26 are located adjacent the corners formed by the opposite sides 19 and 21 with the upper or top side 16 of the rectilinear frame assembly 12.

Since these light distribution and detection assemblies 24 and 26 are identical, their structure will- be described with reference to assembly 24 only. The assembly 24 comprises a light emitting means or source 32, detector means 34 for detecting the level of light present thereat and producing a corresponding or correlative output signal, and light directing means 36 for directing light from the light across or into the target zone 14. As will be seen presently, the directing means additionally directs light returning from the target zone 14 to the detector means 34.

Referring now more particularly to the reflector means or assemblies 18, 20 and 22, as mentioned, each of these reflectors is comprised of a retroreflective material. Such a retroreflective material has a characteristic such that for light received thereby within given limits of angular displacement relative to the surface thereof at the point of incidence, a relatively large percentage of that light will be reflected back along the same path of incidence. In this regard, these angular displacement limits will also be referred to hereinafter as the established or prescribed angular limits of retroreflective operation. As light is incident upon the retroreflective surface outside of these established or prescribed angular limits, the percentage of light which is retroreflected falls off rapidly.

Accordingly, in the illustrated embodiment, each of the retroreflectors 18 and 20 is appropriately arcuately curved and positioned relative to the frame 12 and light distribution and detection assemblies 24 and 26, for assuring that light incident thereupon the opposite one of the light directing means 36 will be retroreflected back to the same light directing means 36. In this regard, it will be seen that the retroreflector 18 retroreflects the light with respect to only the oppositely located light distribution and detecting assembly 26.

In the same fashion, the retroreflector 20 retroreflects light with respect to the oppositely disposed light distribution and detecting assembly 24.

The remaining retroreflector 22 also comprises an arcuately curved strip of retroreflective material which is so curved and positioned with respect to the bottom side 23 of the frame 12 as to reliably retroreflect all light received from both light distribution and detecting assemblies 24 and 26. More particularly, retroreflector 22 receives and returns light with respect to the light directing means 36 associated with each of these assemblies 24, 26.

In operation, objects in the target zone, such as objects 40, 42 and 44 are detected and their locations determined by a geometric or triangulation method. This determination takes into account the relative angles or angular displacements of each of these objects with respect to the detector means 34 of each of the light distribution and detecting assemblies 24 and 26. These angular orientations can in turn be determined by providing a scanning means or assembly for scanning the target zone 14 so as to produce a signal which can be correlated over time with respective angular orientations of portions of the target zone 14 relative to some fixed reference. Such a fixed reference could comprise the corner in which each of the light distribution and detecting assemblies 24, 26 is located.

Referring now to Fig. 2, the scanning means may comprise a housing 50 mounted for rotation between respective front and rear walls 13, 15 of the frame assembly 12. The light directing means here comprises a beam splitter 36 which is angularly disposed, preferably at a 45-degree angle intermediate the housing 50 and the target zone 14. The light source 32 is positioned to one side of the beam splitter 36 as viewed in Fig. 2 and the light emitted therefrom is directed by a suitable lens onto the beam splitter to be redirected substantially at right angles into the target zone 14. Returning light beams, having tra versed the target zone 14, are transmitted through the beam splitter 36 to the detector 34, which in the embodiment of Fig. 2 is dis posed within the housing 50 so as to rotate in unison therewith.A motor 52 is coupled for rotating the housing 50 and detector 34 therein so as to effectively scan the target zone over substantially a 90-degree arc as generally indicated by the beams of light at various angles across the target zone 14 in Fig. 1. An additional lens 54 is also preferably provided for focusing the return beams from the target zone upon the detector 34. Accord ingly, a return beam entering the housing 50 and impinging upon detector 34 at any given point in time may be correlated with the relative angular position of the housing 50 at that point in time to thereby determine the angular orientation of an object, such as one of objects 40, 42 and 44 which cause a change in the received light level at the detector 34 at the same point in time.

Referring now also to Fig. 3, an alternate embodiment of a light distributing and detecting apparatus which may be utilized for both assemblies 24 and 26 in place of the embodiment of Fig. 2 is illustrated. Like reference numerals, together with the suffix a will be utilized to designate like parts and components of the embodiment of Fig. 3. Similarly to the embodiment of Fig. 2, a housing 50a is rotatably mounted between respective front and rear walls 13, 15 of the frame assembly 12. The housing is operatively coupled to be rotated by a motor 52a mounted to one side of the frame 12, which defines a spin axis 56.

The light source 32a is disposed to one side of the housing 50a for directing a beam of light along a primary beam path 58 through a first aperture 60 in the housing 50a. The beam splitter 36a is now located at a 45degree angle intermediate the light source 32a and housing 50a, such that light from the source 32a first passes through the beam splitter 36a before reaching housing 50a.

A mirror 62 is mounted internally of housing 50a for rotation therewith. The mirror 62 is preferably disposed at a substantially 45-degree angle relative to the frame 12 for redirecting light received from the light source 32a substantially at right angles into the target zone 14 as the housing is rotated. It will be noted that the aperture 60 is located substan tally centered upon both the spin axis 56 and the primary beam path 58 so that light from the source 32a enters the housing and strikes the mirror 62 regardless of the angular orientation thereof as the housing is rotated by motor 56. The mirror 62 delivers the redirected light beam to the target zone 14 through a second aperture 64 in the housing 50a.It will be appreciated that the speed of rotation of the housing 50a is sufficiently small relative to the speed of light that a return beam of light from the target zone 14 will substantially instantaneously reenter the housing through aperture 64 and impinge upon mirror 62. The mirror 62 redirects this return beam of light along the primary beam path 58 toward the beam splitter 36a in the opposite direction to the beam emitted by the light source 32a. Beam splitter 36a reflects sub stantialiy one-half of the energy from this return beam, as indicated at reference numeral 66, at substantially a right angle to impinge upon the detector 34a, which is mounted ex teriorally of the housing 50a in the embodiment of Fig. 3.

The assemblies described with reference to Figs. 2 and 3 define but two alternative constructions of a light distribution and detecting assembly which may be utilized in conjunction with the optical position locating device of the invention. It will be understood that alternative constructions and arrangements of light distributing and detecting assemblies may be utilized without departing from the invention, so long as two such assemblies are utilized at opposite corners of the frame 12 as illustrated and described above with reference to Fig. 1.

The assembly illustrated in Fig. 3 is substantially similar to that disclosed in the Applicant's copending U.S. application Serial No.

599,131 filed April 11, 1984.

Claims (10)

1. An optical position locating device comprising: a four-sided, rectilinear frame assembly defining a target zone within which the position of an object is to be located by the device; a pair of light distribution and detecting assemblies respectively located at opposite ends of one side of the frame, each of the light distribution and detecting assemblies comprising a light source, detector means for detecting light and producing a corresponding output signal, and light directing means for directing light from the light source to the target zone; the detecting means being positioned for receiving light from the target zone; and retroreflecting means arranged about the target zone for reflecting incident light along a path substantially coincident with the path of incident light; the retroreflecting means comprising three retroreflective members respectively arranged along a side opposite said one side and both of the other pairs of sides of the target zone; and, scanning means operatively associated with the detector means for determining the angular displacement of light received thereby relative to the target zone, so that the presence of an object within the target zone registers upon the detector means as a change in light intensity at a given angular displacement; whereby the location of an object within the target zone is determined in two dimensions from the respective angular displacements of the changes in light intensity incident upon the two detector means.

2. An optical position locating device according to claim 1, wherein the retroreflective members comprise a first arcuately curved strip of retroreflective material remote from one of one of the light sources and defining an angle of incidence with respect to light from the one light source within prescribed angular limits of its retroreflective operation; a second strip of arcuately curved retroreflective material remote from the other of the light sources and defining an angle of incidence with respect to light from the other light source within prescribed angular limits of its retroreflective operation; and a third arcuately curved strip of retroreflective material arranged on said opposite side and defining an angle of incidence with respect to light from both of the light sources within prescribed angular limits of its retroreflective operation.

3. An optical position locating device according to claim 1 or 2, wherein each of the light directing means also operates to direct reflected light received from the target zone to its associated detector means.

4. An optical position locating device comprising light emitting means; light detecting means for detecting the level of light present and producing a corresponding signal; means defining a substantially rectangular target zone; and light directing means for initially directing light from the light source to the target zone and for directing light returned from the target zone to the detector means; wherein the light emitting means, the light detecting means and the light directing means comprise a light source, a detector means and a light directing means positioned at each of a first corner and a second corner located along a common first side of the target zone; and further including a plurality of reflective means arranged about the target zone and cqmprising first and second reflector assemblies defining facing, opposite second and third sides of the target zone, and a third reflector assembly defining the fourth side of the target zone opposite and facing the first side; each of the first, second and third reflector assemblies comprising retroreflective material.

5. An optical position locating device according to claim 4, wherein each of the first and second reflector assemblies comprises a substantially continuous strip of retroreflective material appropriately curved to receive light along the length of its associated side of the target zone from the light directing means most nearly adjacent the opposite side at an angle of incidence within prescribed angular limits of its retroreflective operation thereof.

6. An optical position locating device according to claim 5, wherein the third reflector assembly comprises a substantially continuous strip of retroreflective material appropriately curved to receive light along the length of the fourth side of the target zone from both of the light directing means at an angle of incidence within prescribed angular limits of its retroreflective operation.

7. An optical position locating device according to claim 4, 5 or 6, and further including scanning means operatively associated with each of the detector means for determining the angular displacement of light received thereby relative to the target zone, such that the presence of an object within the target zone registers upon the detector means as a change in light intensity at a given angular displacement; whereby the locating of an object within the target zone is determined in two dimensions from the respective angular displacements of the changes in light intensity incident upon the two detector means.

8. An optical position locating device according to any one of the preceding claims, wherein each of the light directing means includes a beam splitter.

9. An optical position locating device according to any one of the preceding claims, wherein each of the light sources is stationary and emits a beam of light toward the light directing means to be directed thereby along a primary beam path in first direction; and wherein each of the scanning means comprises a housing, drive means for rotating the housing about a spin axis, and reflective means for redirecting a beam of radiant energy affixed within the housing; the housing having a first aperture substantially centred on the spin axis and on the primary beam path whereby the beam of radiant energy from the light source enters the housing through the first aperture regardless of the rotational orientation of the housing and impinge upon the reflective means; the reflective means being affixed within the housing to redirect the beam of radiant energy through a second aperture in the housing and towards the target zone; such that the beam of radiant energy emerging from the housing through the second aperture sweeps the target zone as the housing is rotated at a given rotational speed; the given rotational speed being sufficiently slow with respect to the speed of light that the light substantially instantaneously re-enters the housing as a return beam through the second aperture to reflect from the reflective means through the first aperture in a second direction substantially opposite to the first direction along the primary beam path; the directing means being arranged to direct the return beam to the detector means.

10. An optical position locating device substantially as described with reference to the accompanying drawings.