Light emitting stylus and user input device using same

The present invention provides a user input device that includes and array of light detectors and a light emitting stylus configured to emit a beam of light detectable by the light detectors. The light beam is wide enough at the plane of the detectors so that at least two detectors are illuminated for all positions of interest. This allows the light beam position to be interpolated to obtain positional resolution that is greater than would be expected simply due to the spacing between detectors. Interpolation can be further aided by using a light beam that has a known variance in cross-sectional intensity. The present invention also provides for determining the orientation of the stylus by comparing the detected shape of the light beam cross-section to the known shape of the light beam cross-section.

This invention relates to a light emitting stylus and the use of a light emitting stylus in a user input device.

BACKGROUND

Touch sensors have become an increasingly common way for users to intuitively interact with electronic systems, typically those that include displays for viewing information. In many applications, the information is viewed through the touch-sensitive area so that the user seems to interact directly with the displayed information. Depending on the technology of the input device, a user may interact with the device using a finger or some other touch implement such as a stylus. When a stylus is used, it can be a passive object (as is typical for those used with resistive touch screens, for example in a personal digital assistant or other hand-held device) or an active object (as is typical for those used with signature capture devices). An active stylus can communicate signals with the input device, whether sending, receiving, or both, to determine touch position or other information. Active styli include those that send or receive radio frequency signals (RF pens), those that use magnetic fields for inductive signal capture (inductive pens), and those that emit or receive light (light pens).

SUMMARY OF THE INVENTION

The present invention provides a light-sensitive user input device that includes a co-planar array of light-sensitive devices disposed to sense light transmitted through an input surface of the input device, nearest adjacent light-sensitive devices having a center-to-center spacing that is no more than a maximum distance, and a stylus configured to emit a light beam detectable by the devices, the light beam exhibiting a cross-sectional profile having a known shape characterized by an intensity variance across the beam profile. The light beam exhibits a size at the plane of the devices that is greater than the maximum distance when the stylus is contacting the input surface. The input device also includes electronics coupled to the devices and configured to determine the position of the light beam to within a spacing that is less than the maximum distance.

The present invention further provides a method of determining the position of a light beam at an input surface. The method includes providing a co-planar array of light-sensitive devices disposed to sense light transmitted through the input surface, emitting the light beam with a known shape characterized by a cross-sectional profile having a known intensity variance, the light beam having a spot size sufficient for the light beam to be detected by at least two of the light-sensitive devices when the light beam is directed through the input surface. The method also includes detecting the light beam by at least two of the light-sensitive devices, and determining the position of the light beam to an accuracy that is less than the center-to-center distance between nearest adjacent light-sensitive devices by interpolating signals measured during the detecting step using the known intensity variance of the light beam.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description that follow more particularly exemplify these embodiments.

DETAILED DESCRIPTION

The present invention relates to a light emitting stylus, the position and states of which can be measured by an optical digitizer. Light beam size and shape can be adapted to provide accurate, high resolution location determination using an array of light sensors.

The present invention provides a light emitting stylus useful in a user input device, where the stylus can include one or more of the following features. The present invention provides a stylus that emits a light beam having a spot size that is greater than the distance between neighboring adjacent optical sensors to locate the beam at all locations of interest. The present invention provides a stylus that emits a known, varying intensity profile, such as with a slightly defocused light beam having an intensity profile that is brightest at the center and reduces to zero in a known pattern. In using such a stylus, two or more adjacent optical sensors can detect light in an amount proportional to their proximity to the center of the beam, thus allowing interpolation of the location of the beam center resulting in a greater resolution than would be expected given the distance between optical sensors. The present invention provides a system in which the angle of the light beam, and therefore the angle of the stylus, can be measured using the aspect ratio of the beam shape at the plane of the light sensors in comparison with the known aspect ratio of the beam. This angle, and the location of the center of the beam, can be used to locate the position of the stylus. This may be particularly useful when the digitizer surface is a significant distance from the light sensing surface to account and correct for parallax errors. Knowing the position of the stylus, and thus the user's hand, can also be useful for other purposes such as determining where to display information so that it can be seen by the user.

FIG. 1shows an input device10that includes a digitizer11, which may include an upper substrate15having an input surface16, a lower substrate18, a photo detector array19including detectors48, and inter-substrate gap17. Digitizer11may also function as a display, for example an active matrix liquid crystal display (AMLCD) where the photo detectors are additionally provided, a liquid crystal display (LCD) where the photo detectors are the pixel transistors of the display, an organic electroluminescent display (OLED) where the light emitting pixels also function as photo detectors, and the like. Examples of digitizers suitable for use in the present invention include those disclosed in the following publications, each of which is wholly incorporated into this document as if reproduced in full: WO 03/071345; WO 03/058588; U.S. Pat. Nos. 6,337,918; 5,838,308; JP 10-187348; JP 10-283113; JP 58-086674; JP 60-198630; JP 60-200388; JP 61-006729; JP 61-075423; JP 11-282628; and JP 2003-66417.

FIG. 1also shows two identical light emitting styli20and21, each emitting highly focused laser-like beams30and31, respectively. Styli20and21are a distance T from array19. Stylus20is perpendicular to array19, and the width of its beam30is sufficient to irradiate at least two photo detectors simultaneously. The location of stylus20can be determined by measuring the position of the spot of light intersecting with detector array19directly below stylus20. Detection of light beam30may be enhanced by modulating beam30so the detected signal can be filtered and separated from ambient light or electronic noise. Light beam30may be modulated by changing color, intensity, duty cycle, polarization, or pulse width modulation without affecting the position measurement. Such beam modulation may also be used to convey states of the stylus, such as the on/off condition of a tip transducer24(e.g., indicating contact of the stylus with the input surface), or side switch23. These states can be communicated via array19to measurement system213(seeFIG. 8). Uniquely modulated beams from two or more styli may be used to distinguish the styli, for example those used by two or more unique users of a single digitizer.

The side switch23and/or the tip transducer24can be pressure activated switches that make or break an electrical contact, resulting in a signal. The signal may be a change in stylus beam30, such as a change in beam intensity, or in the duty cycle of a modulated beam30, or in frequency of modulation of beam30, or the color of beam30, or the polarization of light in beam30. The change in stylus beam30is conveyed via array19to measurement system213where it may be interpreted as the equivalent of a right or left mouse click, or other change in status of stylus20.

Side switch23may be a capacitive sensing transducer that activates when touch contact is made to the body of stylus20and also to an electrically isolated area, identified as switch23. Tip transducer24may be a pressure sensing transducer that outputs a continuously varying signal in response to varying pressure on tip transducer24. The signal from transducer24can cause a change in stylus beam30, such as a change in beam intensity, or frequency, etc. described above.

Tip transducer24may be a mechanical shutter that passes a variable amount of light from a light source in stylus20to array19, depending on the amount of pressure applied to tip transducer24. Tip transducer24may be a light guide in the form of a movable lens or a tube that focuses or guides light to form a variable width beam from a light source in stylus20to array19, depending on the amount of movement of tip24, resulting from pressure applied to tip transducer24. Width changes of the beam can be measured as described with respect toFIG. 5.

Referring again toFIG. 1, stylus21and its beam31are identical to stylus20and beam30, except that stylus21is at an angle of Λ degrees with respect to an axis perpendicular to array19. This angle and the distance T between stylus21and array19results in a distance E between the point of contact of stylus21with surface16and the point where light beam31intersects with detector array19. If the location of stylus21were measured as the intersection of beam31and array19, the distance E will represent an error. The error E can be measured and corrected if the angle Λ of stylus beam31can be measured, and the distance T is known (or can be measured).

FIG. 2shows an overhead view of the array19of photo detectors48, spaced center-to-center at a distance MDhorizontally and NDvertically. As shown, ND=MD, although this condition need not be the case. The present invention contemplates any array or distribution of light detectors, including linear arrays, hexagonal arrays, rectangular arrays, or any other suitable array or distribution of detectors.FIG. 2is meant to represent a relatively high detector density such as is typical of OLED displays configured for optical sensing, such as disclosed in WO 03/058588, incorporated herein by reference. Also shown are light spots40and41irradiated by stylus beams30and31respectively. A resolution of half the detector array19spacing (in this case M/2), can be achieved if a beam irradiates at least portions of two detectors simultaneously in each of the X and Y directions. Each photo detector in array19measures multiple levels of light, so interpolation of light levels can be used to locate the position of a spot having a diameter greater than 2M diameter to a resolution finer than the inter-detector distance M. In the case where NDand MDare not equal, it may be desirable for the spot diameter to be about equal to or greater than the larger of NDand MD. While beam spot40is shown to be round, it will be appreciated that any spot shape can be used, particularly when the spot shape and intensity distribution are known.

Spot41is made by a round beam of light from stylus21that is oriented at an angle of Λ degrees from the plane of detector array19. The resulting spot41is an elliptical shape with minimum width D, equal to the diameter of beam31. The long dimension L of the ellipse is determined by the equation:
L=D*Cos Λ  (Equation 1)
So Λ can be calculated from L and D;
Λ=Cos−1D/L(Equation 2)

A stylus beam angle of 45° results in L=1.41*D. The length to width ratio and orientation of the longer dimension of elliptical spot41can thus be used to measure the tilt angle Λ and tilt axis of stylus21. Given the angle Λ from equation 2 and the known distance T, the magnitude of error E can be calculated by:
E=Tan Λ*T(Equation 3)

The magnitude of error E can be calculated from Equation 3. The long axis L of elliptical spot42, and therefore error E, can be determined directly from sensor array19measurements and simple image recognition algorithms. The direction of error E, however, cannot be determined from direct, static measurement. For example, spot41may result from a stylus21at position Q, or at position W. The actual stylus position can be determined by applying one or more of several methods, examples of which are outlined below.

Stylus21will typically be hand held, and thus the tilt angle Λ of stylus21will typically be in the direction of the hand or fingers holding the stylus. Since the user and hand are typically oriented toward the bottom of digitizer array19, it may be assumed that the hand, and (generally) stylus21are located nearer to point W than to point Q. This method may be adequate in systems where the orientation of the input device with respect to a user will always be known.

Since digitizer array19senses light, hand position may be determined by measuring the shadow47cast by stylus21and the hand or fingers, relative to light spot31. A shadow49to the right of spot31(as shown inFIG. 1), indicates that stylus21is located nearer to point W than to point Q. This method may be adequate in systems where there is sufficient ambient light to cast a shadow from the stylus or the hand.

It is also possible to infer the hand location based on spot movements. In normal writing, few strokes (especially straight strikes) are made by pushing the stylus in the direction it is pointing. Most strokes will be made sideways or by pulling the stylus tip in the direction the stylus is tilted. Thus, a recent history of relative beam locations can be used to determine hand position.

A further method includes prompting the user to indicate hand position and/or device orientation prior to user inputs being made.

A further method of determining stylus orientation includes additional analysis of the light distribution of the spot formed on the detectors. Without loss of generality, in the case in which a light beam having a know cross-sectional intensity distribution, such as a Gaussian light distribution or a conical light distribution, illuminates the sensor array at an angle, an elliptical spot will be formed such as spot41inFIG. 2(and, analogously, as shown inFIGS. 5 and 7with respect to spots141and341, respectively). The elliptical spot will generally exhibit an intensity distribution such that the half of the spot oriented toward the stylus tilt direction will have a higher integrated intensity than the half of the spot oriented away from the stylus tilt direction. As such, comparing the integrated intensity contribution from different halves, quadrants, or other selected sections of the spot can be used to indicate stylus tilt direction.

In addition to aiding positional error corrections, hand and stylus position information can be used for other purposes. For example, when popping up a menu or other information on the display, it may be desirable to position the information where its viewing is unlikely to be blocked by the stylus or hand. As another example, in multiple user systems, the determined position and orientation of the stylus can be used to determine which user is inputting the information.

FIG. 3shows an input device110similar to device10shown inFIG. 1, except that styli120and121emit conical beams, spreading light in spot patterns over a wider area. Also, sensor array119has fewer detectors148that are more widely spaced, as may be the case where the photo detectors148are part of a photo-sensitive LCD, as disclosed in International Publication WO 03/071345, which is hereby incorporated by reference. In a sparse array such as119, a wider beam with a known varying intensity across its axis has advantages as discussed below.

FIGS. 4(a) and (b) can be used to demonstrate various representative beam intensity profiles.FIG. 4(a) shows chart100, with light distributions of several light beams shown. The distribution of radiant intensity around a light source (e.g. an LED) is referred to as the beam angle Φ. The maximum radiant intensity is on the optical axis. This is generally reduced as the angle Φ to the optical axis increases. The range of the optical angle within which the radiant intensity is greater than or equal to 50% of the maximum value is referred to as the half intensity value.

Referring to graph100, line101results from a sharply focused laser-like beam with a half intensity angle near zero. Line102is typical of an unfocused, planar type LED, with a half intensity angle of +/−60°. Line103may be achieved with a parabolic lens on an LED, resulting in a half intensity angle of +/−25°. Graph90inFIG. 4(b) shows another view of line103, the relative radiant intensity of a light source with half intensity angle of 25°. Such a known beam intensity profile can be used as described in discussions that follow.

Referring back toFIG. 3, consider that the beam of stylus120has the radiant versus angle as indicated by profile103inFIGS. 4(a) and (b). This results in light distribution onto array119that varies with distance from a maximum light at the beam130center, reducing with distance from the center in a known way. When used with a sparse array such as array119, this light distribution has several advantages over highly focused beams30and31, shown inFIG. 1. Because the intersection of beam130with array119is wider, the light irradiates several detectors148even though their spacing is wide. The light distribution has a defined pattern, which may be used to more accurately interpolate between widely-spaced detectors148. Also, changes in distance between stylus120and array119will result in a change in width of the intersection of beam130and array119that may be detected. This may allow stylus120height (distance from array119) to be measured.

FIG. 5shows a top view of array119and light spots140and141irradiated by stylus beams130and131, respectively. Inter-detector spaces are MShorizontally and NSvertically, where MS=NS. G represents the width of the minimum gap between adjacent photo detectors148. Spot42is an example of a spot that might be made by a small diameter, more sharply focused laser-like beam. If spot42diameter is less than or equal to the inter-detector gap G (as shown), it can be located by detectors in array119with a resolution determined by the inter-detector distance M. If spot42diameter is greater than the inter-detector gap G, it can be measured simultaneously by two detectors140, and interpolation can be used to locate spot42with a resolution of M/2. The inter-detector spacing M of sparse array119may be greater than 1 mm, so a resolution of M/2 would be marginal for some stylus applications such as writing. Therefore a wider, variable-intensity spot like140can be generated so interpolation can be used more effectively.

Referring again toFIGS. 3 and 5, consider spot140having a light distribution as defined by profile103shown inFIGS. 4(a) and (b), and spot140is centered half way between detectors142and143. Given M=N=1 mm, and T=3 mm, detectors142and143will receive about 0.94 of the maximum light transmitted to the plane of the detectors. Detectors144and145will receive about 0.66 of maximum, or 70% as much as detectors142and143. Detectors146and147will receive virtually no light. These light intensities and intensity differences among adjacent detectors allow high resolution interpolation between the detectors in that the beam intensity profile and overall shape are known and can be compared to the detected signals. The detected signals can be mapped onto the known profile and shape to pinpoint the location of the center of the beam.

Elliptical spot141results from stylus121, at an angle Λ2with respect to array119. Length to width ratios can be used to calculate the orientation and angle of stylus121, and the error E2, using methods similar to those described above in terms of stylus21and elliptical spot41. Error E2may also be further analyzed. A beam with light distribution as defined by profile103will distribute light with half of total irradiation on either side of the optical axis (and stylus axis). The irradiation falling in the direction of stylus tilt will fall in a smaller area that spans length E2, while the irradiation on other side of the optical axis will cover a larger area. The total illumination in the region of spot141collected by detectors148may be analyzed to determine the location of the optical axis, based on a 50%/50% distribution. Alternatively, the optical axis may be located by comparing the measured light distribution of spot141versus the known light distribution profile (e.g., profile103inFIG. 4(b)).

FIG. 6shows an input device310including digitizer311. Two identical light emitting styli320and321are also shown, each emitting focused beams330and331with an annular beam pattern. Stylus320is shown in cross section, showing internal light source335, and the cross section of tubular shaped light guide336, which carries light from source335through tip324, focusing it into an annular pattern of light. Stylus321projects a similar light pattern at an angle Λ3.

FIG. 7shows an overhead view of array319of photo detectors348. Also shown are ring shaped light spots340and341irradiated by stylus beams330and331, respectively. The ring-shaped spot340has the advantage that it can be formed of a relatively highly focused beam while exhibiting high contrast in light level, and thus in signal, between adjacent detectors. This contrast can be detected on both the inner and outer edges of the ring. For example, detector350will detect low light, while the eight nearest neighbor detectors adjacent to350will detect higher light levels, and the next group of detectors outward from the eight detectors will detect low light. Image detection algorithms can be used to resolve the stylus location with high resolution. The height of stylus330may also be measured using a ratio of ring diameter to center (unlit) diameter. The tilt angle and axis of elliptical ring shaped spot341can be determined as described above for spot41inFIG. 2.

Hand shadow349and stylus shadow347can be used to determine the tilt angle Λ of stylus321. In situations where spot contrast is low, shadows349and347can also be used in conjunction with spot341to locate the stylus.

The spot intensity profiles shown and discussed are illustrative and not meant to be limiting. Other known, varied spot intensity profiles can be used in addition to those shown in the drawings, and are fully contemplated for use with the present invention as will be appreciated by those of skill in the art from the description provided in this document. The techniques for spot location determination and enhanced resolution, beam angle determination, stylus orientation determination, and so forth, as described are directly applicable to any spot intensity profile having characteristics detectable by light sensor arrays useful in the present invention.

FIG. 8shows a block diagram of a display system with a photo detector array. Generally, the display pixel array210and the photo detector array212are co-located as described in published U.S. Patent Application US 2003/0122749 and in International Publication WO 03/071345, each of which is hereby incorporated into this document as if reproduced in full. Pixel drivers211and the photo detector measurement system213may also be integrated into the same semiconductor device(s), and may be in communication with system controller218. Display pixel drivers211are known in the art. Photo detector measurement system213can measure the amount of light irradiating each detector in display pixel array210. It may also be able to measure ambient light and to discriminate between ambient light and shadows. A system controller calculates display information to be sent to pixel drivers211, and also calculates the position of light patterns on photo detector array212, measured by photo detector measurement system213.

FIG. 9shows a cross sectional view of system410with digitizer411having detector array419. Each detector448in array419has an associated lens, for example lenses452,453,454,455,456, and457, in its optical path. A similar lens arrangement is disclosed in U.S. Pat. No. 6,028,581, which is incorporated by reference herein. Lenses452through457focus light from above digitizer411such that each detector in array419receives light nominally perpendicular to array419, through a column equal in diameter to lenses452through457. Light431from stylus421is spread in a wide angle, for example 170 degrees, so it is spread across many detectors, and may strike the detectors at various angles as indicated inFIG. 9. Lenses452through457convey perpendicular light to their respective detectors, so only the light impinging on lenses455and456would be focused onto any detectors. Thus, the error E4between the tip location of stylus421and the center of its emitted light spot, due to angle Λ4of the stylus, can be reduced.

A lens above each detector in array419can also increase the contrast of light and shadows received by detectors in array419, because light impinging on surface416of digitizer411at oblique angles will be refracted by the lenses away from detectors in array419. This is particularly important where shadows, such as those cast by the stylus or hand as described in this document, are used to locate stylus and/or touch positions.