GB2263009A - Write on display - Google Patents

Abstract

A system which determines the location of a stylus (14) relative to a screen (12). The screen (12) has a transparent plate that covers a liquid crystal display. Attached to the edges of the plate are transducers (24, 28) that create waves that propagate across the plate. An excitation circuit is connected to the transducers to coordinate and initiate the waves. The system also includes a stylus (14) that can be pressed against the plate by the user which detects the presence of the waves and sends a detection signal to a computation circuit, which determines the time for the wave to travel from the transducer to the stylus. The location of the stylus (14) relative to the plate is then computed by the computation circuit. The transducers may be arranged to produce waves that alternately travel on the x and y - axis of the plate. The plate may be constructed from a plurality of fibre optic elements. <IMAGE>

Description

IJRITE ON DISPLAYI~InlNO DISTORTION.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system that can determine the location of a stylus relative to a video screen, as a user moves the stylus about the screen.

2. Description of Related Art Displaying lines or characters on a computer screen typically requires the typing of keys or the manipulation of a mouse. It has become increasingly desirable to "write directly onto the screen with a stylus or an electronic pen.

With such an arrangement the computer screen operates like a piece of paper, greatly simplifying the use of the computer.

One approach to creating a write on display is to propagate a wave along the surface of the screen to detect the location of a stylus. As the user moves the pen about the screen, the system computes the amount of time it takes the wave to reach the stylus. Knowing the velocity of the wave, the location of the stylus can be computed. The surface waves are generated in two perpendicular directions, so that the exact position of the stylus relative to the screen can be determined. The screen is typically constructed from glass which is subject to pitting and scratching. Such imperfections can distort the surface waves and reduce the accuracy of the system.

It would be desirable to incorporate a liquid crystal display (LCD) into a "write on" screen. LCDs are much lighter and thinner than raster based monitors.

Unfortunately, liquid crystals are very sensitive to pressure. When a user presses the stylus onto the screen, the pressure of the pen distorts and changes the polarizing characteristics of the liquid crystals, so that a blackish amorphous shape appears around the stylus. One obvious solution is to make the screen thicker, but a thick screen creates paralax and other optical distortions. It would therefore be desirable to have an accurate, low distortion write on screen that can utilize a LCD.

SpDnNNEt~ OF~ YE The present invention is a low distortion write on display, that includes a system which can determine the location of a stylus relative to a screen. The screen has a transparent plate that covers a liquid crystal display.

Attached to the edges of the plate are transducers that can create volumetric waves that propagate across the plate. The transducers are typically arranged so that the volumetric waves alternately travel across the x and y axis of the plate. An excitation circuit is connected to the transducers to coordinate and initiate the volumetric waves.

The system also includes a stylus that can be pressed against the plate by the user. The stylus has a sensor that detects the presence of the volumetric waves. The sensor sends a detection signal to a computation circuit, which determines the time that it took for the volumetric wave to travel from the transducer to the stylus. The location of the stylus relative to the plate is then computed by the computation circuit.

The volumetric waves propagate independently of the surface conditions of the plate, such that scratches or other surface imperfection do not effect the accuracy of the system. The plate is preferably constructed from a plurality of fiber optic elements. The fiber optic plate is thick enough to prevent any distortion of the liquid crystals by the pressure of the pen, without creating any optical distortion through the plate. The fiber optic plate provide a visual image that appears to be at the top of the screen.

The present invention thereby produces a write on display that has the characteristic of actually writing on a piece of paper.

Therefore it is an object of this invention to provide a write on display with low optical distortion.

It is also an object of this invention to provide an accurate write on display that is not susceptible to any degradation of the screen surface.

It is also an object of this invention to provide a write on display that incorporates a liquid crystal display that is not subject to deformation from the pressure of a stylus.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the present invention will become more readily apparent to those skilled in the art after reviewing the following detailed description and accompanying drawings, wherein: Figure 1 is a perspective view of the system of the present invention having a screen and a stylus; Figure 2 is a circuit diagram of the system of Fig. 1; Figure 3 is cross-sectional view of the screen of Fig.

1; Figure 4 is a cross-sectional view of a stylus of the system of Fig. 1.

##T AlL DESCElE5IoR Referring to the drawings more particularly by reference numbers, Figure 1 shows a system 10 of the present invention.

The system 10 has a screen 12 and a stylus 14. The stylus 14 is preferably shaped as a pen so that a user can easily grasp and move the stylus 14 relative to the screen 12. The screen 12 is typically attached to a housing 16 and is integrated into a computer 18. The stylus 14 may be connected to the computer 18 through a wire 20. Alternatively, the stylus 14 may be remotely coupled to the computer 18 through light, radio or any other mode of signal transmission.

The screen 12 is typically rectangular in shape and is oriented in an x, y and z cartesian axis coordinate system.

Attached to one edge 22 of the screen 12 is a first transducer 24. Attached to a second edge 26 of the screen 12 is a second transducer 28. The transducers 24 and 28, create volumetric waves, commonly referred to as Lamb waves, that propagate across the screen 12. The transducers are typically constructed from a piezoelectric material which becomes mechanically strained when a voltage is applied to the material. The displacement of the piezoelectric induces the Lamb waves in the screen 12. Although one first transducer 24 and one second transducer 28 are shown, it is to be understood that the transducers 24 and 28 can actually be a plurality of transducers attached to the edges of the screen 12. Additionally, the transducers 24 and 28 may be attached to the top surface 30 of the screen.It being found that volumetric waves can be created if the thickness of the screen 12 is of the same order as the wavelength of the wave.

The first transducer 24 creates a volumetric wave that propagates along the x axis of the screen 12. The second transducer 28 induces a Lamb wave that travels across the y axis of the screen 12. The stylus 14 then detects the wave as it passes underneath the pen 14. The frequency of the waves through the screen 12 is a known constant, so that the distance from the transducers to the stylus 14 can be calculated by determining the time it takes the wave to reach the pen 14. The excitation of the transducers 24 and 28 are preferably timed so that the wave along the y axis is not generated until the wave along the x axis has traversed the screen 12, and vice versa. This timing arrangement prevents interference between the waves, which could provide a false signal to the stylus 14.

Figure 2 shows an electrical circuit 32 that can be used with the present invention. The circuit 32 has a pulse generator 34 that provides isochronous pulses to both a counter 36 and a demultiplexer 38. The demultiplexer 38 channels the pulse signal either to the first transducer 24 or the second transducer 28, depending on the state of the select input to the demultiplexer 38. The select input changes state each time the pulse generator 34 provides a pulse, such that the demultiplexer 38 alternately channels the pulse signals to the first 24 and second 28 transducers.

For example, the select input to the demultiplexer 38 may be connected to the output of a flip-flop (not shown) that has an inverted output tied to its own input. The flip-flop is clocked by the pulse generator 34, so that every time a pulse signal is generated, the flip-flop changes states and the demultiplexer 38 changes channels.

The pulse signals are amplified by first 40 and second 42 amplifiers. The amplifiers provide a large voltage gain, so that a detectable Lamb wave is generated in the screen 12.

When the waves pass under the pen 14, a voltage, or a change in voltage, is created in the stylus 14 and amplified by a third amplifier 44. The voltage is then provided to a threshold detector 46, which sends a digital signal to the counter 36.

The counter 36 is enabled by the pulse generator 32 and counts until the digitized signal is received from the threshold detector 46. The counter 36 essentially counts the time that it takes the wave to travel from the excited transducer to the stylus. The counter 36 can be connected to a first register 98 and a second register 50 which store the count data. The first register 48 stores the data associated with the excitation of the first transducer 24 and the second register 50 stores the data correlating to the wave generated by the second transducer 28.

The circuit 32 may have a second demultiplexer 52 which channels the data in synchronization with the first demultiplexer 38. That is, when the first demultiplexer 38 channels the pulse signal to the first transducer 24, the second demultiplexer 52 channels the data from the counter 36 to the first register 48. In the alternative, the write lines of the registers can be coupled to the output of the first demultiplexer.38, so that the pulse signal channeled to each particular transducer, also enables the write line of the respective register. The registers 48 and 50 are connected to a microprocessor 54 that can retrieve the data stored and multiply the time counted, by a known constant (phase velocity of the wave) to calculate the distance between the excited transducer and the stylus.

In operation, the pulse generator 32 generates a pulse signal which is directed by the demultiplexer 38 to the first amplifier 40. The signal is amplified and sent to the first transducer 24, which then induces a volumetric wave in the screen 12. At the same time, the counter 36 is enabled and begins to count in increments of time. The wave travels across the x axis of the screen 12. If the pen 14 is pressed into operative contact with the screen 12, the stylus 14 will provide a detection signal when the wave passes under the pen 14. The detection signal is amplified by the third amplifier 44 and sent to the threshold circuit 46, which disables the counter 36. The count is stored in the first register 48, where it can be retrieved and processed by the microprocessor 54.The first pulse signals also provide a select input to both demultiplexers, so that the devices channel the next pulse signal and data to the second transducer 28 and the second register 50, respectively.

The pulse generator 32 then sends another pulse signal to the demultiplexer 38 which channels the signal to the second amplifier 42 and second transducer 28. The second transducer 28 creates a volumetric wave that moves along the y axis of the screen 12. The y axis wave is detected by the stylus 14 which triggers the threshold circuit 46 to disable the counter 36. The y wave count is stored in the second register 50, where it can be retrieved and processed by the microprocessor 54. The pulse signal switches the demultiplexers back to the first transducer 24 and first register 48, and the process repeats itself. The microprocessor 54 determines the x and y coordinates of the stylus 14 relative to the screen 12. The computer 18 may have means to store the coordinates of the stylus 14 as the pen 14 is moved about the screen 12 by the user.The computer 18 may also illuminate that part of the screen 12 which correlates with the calculated x and y coordinates, so that it appears to the user that he is writing on the screen 12 of the computer 18.

Figure 3 shows a preferred embodiment of the screen 12.

The screen 12 has a first plate 56 adjacent to a plurality of liquid crystals 58. The first plate 56 is constructed from a plurality of fiber optic elements 57, that allow light to transmit through the plate 56 with minimal distortion. In the preferred embodiment, there are typically 1,000 optic elements per inch. The transducers 24 and 28 are attached to the edges of the first plate R5 and induce the the Lamb waves to propagate across the plate 56. The plate 56 is stiff enough to prevent the pressure of the stylus 14 from straining and distorting the liquid crystals 58. The low distortion of light as it passes through the first plate 56, provides the optical appearance that the images formed by the liquid crystals 58 are on the top surface of the screen 12.

When combined with the stylus locating feature, the user has the illusion that he is writing on a piece of paper.

The liquid crystals 58 car. be attached to a second plate 60. The second plate 60 is transparent to visible light and is preferably constructed from plastic or glass. The liquid crystals may be etched and attached to the second plate 60 and then coupled directly to the first plate 56. Conversely, the crystals may be etched and attached to the first plate 56 and then coupled to the second plate 60. As an alternate embodiment, the present invention may be used with existing LCD displays that have front and back transparent plates.

The first plate 56 is then attached to the front plate of the LCD display and optically coupled to the crystals by a material such as mineral oil, which covers the front plate and separates the first plate 56 from the LCD display. A back light (not shown) directs light through the second plate 60 and into the liquid crystals 58. By applying voltage signals to the crystals 58, the crystals 58 can be polarized to be either opaque or transparent, as is known in the art.

Although the liquid crystals 58 are shown and described as being attached to the second plate 60, it is to be understood that the crystals 58 could be connected to the first plate 56 and the second plate 60 can be eliminated.

Figure 4 shows a stylus 14 that has a sensor 62 which can detect the volumetric wave as it passes under the pen 14.

The pen 14 has a needle 64 that can move relative to a housing 66 in the directions indicated by the arrows. The needle 64 is attached to a spring 68 that abuts against an upper flange 70 in the housing 66. When the stylus 14 is pressed into contact with the screen 12, the needle 64 is pushed toward the the upper flange 70. When the stylus 14 is removed from the screen 12, the spring 68 moves the needle 64 back into the original extended position.

The sensor 62 includes a piezoelectric strip 72 that has first 74 and second 76 electrodes attached to each end of the strip 72. The first electrode 79 is mounted to a lower flange 78 in the housing 66. The needle 64 has a base portion 80 that abuts against the second electrode 76, when the stylus 14 is pressed against the screen 12. When the volumetric wave passes under the stylus 14, the displacement of the screen 12 moves the needle 64 further into the housing 66. The movement of the needle 64 causes a strain in the piezoelectric strip 72, which creates a voltage between the electrodes 74 and 76 that is detected by the circuit 32. The threshold circuit 46 can be constructed such that the counter 36 is not disabled until a voltage with a minimum predetermined value is induced between the electrodes. Such a threshold circuit prevents any unwanted low level disturbances in the screen 12, from inadvertently disabling the counter 36 and providing an improper location of the pen 14.

While certain exemplary embodiments have been described in detail and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the present invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.

Claims (14)

CLAIFIS

1. A screen, comprising: a first plate that is transparent to visible light; transducer means operatively connected to said first plate for creating volumetric waves in said first plate; a stylus adapted to be held by a human hand and to be brought into contact with said first plate, said stylus being constructed to detect said volumetric waves when said volumetric waves pass under said stylus; and, circuit means operatively connected to said transducer means and said stylus for exciting said transducer means to induce said volumetric waves in said screen, and for computing the location of said stylus relative to said first plate upon detection by said stylus of said volumetric waves.

2. The screen as recited in claim 1, wherein said first plate is constructed from a plurality of fiber optic elements.

3. The screen as recited in claim 1, further comprising a plurality of liquid crystals adjacent to said first plate.

4. The screen as recited in claim 3, further comprising a second plate attached to said liquid crystals, such that said second plate is separated from said first plate, said second plate being transparent to visible light.

5. The screen as recited in claim 1, wherein said first plate has an x axis and a y axis, said transducer means include at least one first transducer that induces an xvolumetric wave along said x axis of said first plate, and at least one second transducer that induces a y-volumetric wave along said y axis of said first plate, said circuit means providing alternating pulses to said first and second transducers such that said x-volumetric waves and said yvolumetric waves sequentially propagate across said first plate.

6. The screen as recited in claim 1, wherein said transducer means is attached to at least one edge of said first plate.

7. The screen as recited in claim 1, wherein said stylus is constructed to detect a displacement of said first plate as said volumetric wave passes beneath said stylus.

8. A screen, comprising: a first plate having a plurality of fiber optic elements; a plurality of liquid crystals adjacent to said first plate; transducer means operatively connected to said first plate for creating volumetric waves in said first plate; a stylus adapted to be held by a human hand and to be brought into contact with said first plate, said stylus being constructed to detect said volumetric waves when said volumetric waves pass under said stylus; and, circuit means operatively connected to said transducer means and said stylus for exciting said transducer means to induce said volumetric waves in said screen, and for computing a location of said stylus relative to said first plate upon detection by said stylus of said volumetric waves.

9. The screen as recited in claim R, further comprising a second plate attached to said liquid crystals, such that said second plate is separated from said first plate, said second plate being transparent to visible light.

10. The screen as recited in claim 8, wherein said first plate has an x axis and a y axis, said transducer means include at least one first transducer that induces an xvolumetric wave along said x axis of said first plate, and at least one second transducer that induces a y-volumetric wave along said y axis of said first plate, said circuit means providing alternating pulses to said first and second transducers such that said x-volumetric waves and said yvolumetric waves sequentially propagate across said first plate.

11. The screen as recited in claim 8, wherein said transducer means is attached to at least one edge of said first plate.

12. The screen as recited in claim 8, wherein said stylus is constructed to detect a displacement of said first plate as said volumetric wave passes beneath said stylus.

13. A screen, comprising: a first plate having an x axis and a y axis, said first plate further having a first edge and a second edge and being constructed from a plurality of fiber optic elements; a plurality of liquid crystals adjacent to said first plate; a second plate attached to said liquid crystals and separated from said first plate, said second plate being transparent to visible light; at least one first transducer operatively connected to said first edge of said first plate, said first transducer being capable of creating x-volumetric waves along said x axis of said first plate; at least one second transducer operatively connected to said second edge of said first plate, said second transducer being capable of creating y-volumetric waves along said y axis of said first plate; ; a stylus adapted to be held by a human hand and to be brought into contact with said first plate, said stylus being constructed to detect said x-volumetric waves and said yvolumetric waves when said x-volumetric waves and said yvolumetric waves pass under said stylus; and, circuit means operatively connected to said stylus and first and second transducers for alternatively exciting said first transducer and said second transducer such that said xvolumetric waves and said y-volumetric waves sequentially propagate across said first plate, and for computing the location of said stylus relative to said first plate upon detection by said stylus of said x-volumetric waves and said y-volumetric waves.

14. A screen substantially as hereinbefore described with reference to the accompanying drawing.