Patent Application
20110134079
This application claims priority from United Kingdom Application for Patent No. 0921216.8 filed Dec. 3, 2009, the disclosure of which is hereby incorporated by reference.
This application relates to touch sensitive screens and in particular touch sensitive screens capable of resolving simultaneous touches at multiple points which are also pressure sensitive.
Touch screen systems implementing both multi-touch and pressure sensitive functionality are rare due to the difficulty in solving technical problems presented while maintaining cost-effectiveness. Reliably detecting the touch locations of multiple points, and their corresponding pressure levels, while ensuring that the quality of the display is not compromised by any screen overlays, presents a significant hurdle for most touch screen technologies.
Known touch screen technologies, and their known drawbacks, include:
There is a need in the art to address the issue of pressure sensitivity in multi-touch touch-screens.
In a first aspect there is provided a display comprising a touch sensitive surface, at least one radiation source and at least one corresponding sensor such that said display can determine by sensing radiation levels in a sensing plane substantially parallel with said surface, the position on said surface of one or more touches by an object, wherein said touch display is operable to determine the relative pressure applied to the touch sensitive surface by a touch based upon a parameter related to the approaching speed of the touching object.
The approaching speed of the touching object may be determined by determination of the rate of change of said parameter from two or more frames imaged between the time said object enters the sensing plane and the time it touches the surface. Said parameter may comprise light intensity, and specifically the light intensity on the portion of the sensor affected by the touching object. Said sensor may comprise an array of individually addressed pixels and said device may be operable to determine the point of lowest intensity and to monitor movement of this point of lowest intensity during said two or more successive frames. Alternatively or in addition said device may be operable to determine said rate of change of intensity from the rate of change of the slope at one or more points on a light intensity profile across said array and/or the rate of change of the width between pixels registering the same intensity levels at one or more points on said light intensity profile. For example, one measurement point may be the midpoint between a touch threshold corresponding with the sensing plane and a minimum touch point corresponding with the display surface.
Said device may comprise said at least one radiation source and said at least one corresponding sensor arranged to emit in and detect radiation from said sensing plane. There may be first and second sets of radiation sources, each with corresponding sensors, both sets of radiation sourced emitting radiation in the sensing plan, said first set emitting radiation in a direction perpendicular to the second set. Said radiation sources and sensors may work together in either absorption, retro-reflective or imaging modes. “Sets” of radiation sources and sensors may include a single radiation source and/or sensor.
Said device may be operable to offset the integration phases of said first set of radiation sources and corresponding sensors in relation to said second set. Said offsetting should be such that only one of said first and second sets of radiation sources is turned on, and integration only performed on data from the corresponding set of sensors, at any one time. In a preferred embodiment, both of said offset integration phases for said first and second sets of radiation sources and corresponding sensors, should be performed in a total timeframe similar to that when performing said phases simultaneously. As a consequence said single integration phase speed may be substantially doubled in comparison to that practicable should integration be simultaneously performed on data from both sets of sensors
Said touch sensitive surface may be separately sensitive to two or more simultaneous touches, and may be able to determine each position of said two or more simultaneous touches.
In a further aspect there is provided a display comprising a touch sensitive surface and first and second sets of radiation sources each with corresponding sensors, said radiation sources being arranged to emit radiation in a single sensing plane substantially parallel with said surface, said first set being operable to emit radiation perpendicular to the second set, such that said device can determine by sensing radiation levels in a sensing plane parallel with said surface, the position on said surface, of one or more touches by an object, wherein said device is operable to offset the integration phases of said first set of radiation sources and corresponding sensors, in relation to said second set.
Said offsetting should be such that only one of said first and second sets of radiation sources is turned on, and integration only performed on data from the corresponding set of sensors, at any one time. Both of said offset integration phases for said first and second sets of radiation sources and corresponding sensors, may be performed in a total timeframe similar to that when performing said phases simultaneously. As a consequence said single integration phase speed may be substantially doubled in comparison to that practicable should integration be simultaneously performed on data from both sets of sensors
Said touch sensitive surface may be separately sensitive to two or more simultaneous touches, and may be able to determine each position of said two or more simultaneous touches.
Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which:
The system actually consists of two sensor arrays 180X, 180Y (
The illumination optics 150 are used to focus and evenly distribute the light output 160 from the LEDs 140, across the screen along the respective axis, and onto the imaging optics 170 which in turn focuses the light onto the pixel array 180.
The z-dimensions of the imaging and illumination optics 170, 150 determine the height of the z-plane detection zone 120. The imaging and illumination optics should be matched in z-height to maximize the percentage of light from the illumination LED which is received by the pixel.
The inventor has determined that such a device can be made sensitive to the vertical (z-dimension) speed at which the contacting object 110 (e.g. a finger) approaches the screen 100, which in turn can be used to emulate sensing of the pressure applied to the screen 100 by said object 110.
When the contacting object 110 breaks the z-plane detection limit 120 of the optics 150, 170, it begins to block the light 160 directed at the pixel array 180, reducing the intensity levels recorded at the end of the frame for the affected pixels. When the contacting object 110 makes contact with the surface 100 of the screen, the light levels of the pixels 180 in the affected area will be at their lowest levels.
The speed sensing function may be performed by the processing unit through analysis of the movement of the detected minimum of a touch point for several successive frames and using this data to derive the speed of the contacting object. A number of frames, dependent upon both the frame rate of the system and the average velocity of the contacting object towards the screen while within the z-plane detection zone, between the contacting object first entering the z-plane detection zone and reaching the surface of the screen can be captured by the x and y sensors and stored in a memory bank. The speed of the contacting object moving through the z-plane detection zone can be shown to be directly proportional to the rate of change of light intensity of the pixels whose light intensity levels are affected by the contacting object blocking the projected light incident on them. Frames imaged between the time the object touches the surface and the time it leaves the sensing plane may also be used in a similar manner to those imaged before contact of the touching object to determine release ‘pressure’ for the detected touch co-ordinates.
The light intensity profiles of the stored frames allow processing unit calculation of the rate of change of minimum light intensity for the detected touch point to be made. The speed of the detected touch is output as a proportionally scaled value based on the rate of change of light intensity. The rate of change of width at one or more points, such as the halfway points between the maximum and minimum levels or the points of maximum positive and negative slopes, can also be used to derive the speed either separately from or in conjunction with the minimum point.
The accuracy of the speed sensing depends upon the number of frames captured while the contacting object is within the z-plane detection zone as a finer the temporal resolution will allow a greater number of samples of pixel data to be captured and hence improve the accuracy of the touch speed calculation. The temporal resolution of the system can be effectively doubled by doubling the clock frequency and offsetting the phases of the frames of the sensors so that when the X-sensor is in the reset & image readout phase, the Y-sensor will be in the integration phase.
When both sensors have a light intensity profile for one or more touch points that is uncorrupted by close proximity of another point or vertical or horizontal alignment of the touch points; the data for a detected touch point from each sensor can be scaled and interpolated to form a single light intensity profile for a touch point with twice the temporal resolution of the data in the frames when compared with a system with the sensors' phases running synchronously.
The above embodiments are for illustration only and other embodiments and variations are possible and envisaged without departing from the spirit and scope of the invention. For example the actual type of touch sensitive screen is not relevant so long as it is of a type that uses the principle of sensing radiation levels in a plane parallel with a screen surface.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0921216.8 | Dec 2009 | GB | national |
