A WRITING PAD FOR ENTERING INFORMATION INTO A DATA PROCESSOR

Abstract: A writing pad (10) in which a grid of electrical elements defines an array of discrete locations (30) on the writing surface (12) with a density of preferably 100 x 50 = 5000 locations (30) per square inch, and digital circuitry is connected to the grid to determine the locations (30) at which writing stimuli are being received. In other aspects, circuitry is used to identify the upper and lower boundaries along one dimension of the writing surface (12), of a local region at which writing stimuli are being received; the writing surface (12) is scanned to identify the coordinate value along one dimension of a point (30) at which writing stimuli are being received, by scanning respectively different predetermined portions of the writing surface (12) along that one dimension, all of the portions being scanned simultaneously; a local zone is defined in the vicinity of an identified point of touching (30), and limits the scanning to that local zone; and a portion of the writing surface (12) includes key zones and a particular digital symbol is generated in response to writing stimuli being received at any of the locations corresponding to one of the key zones.

Description: This invention relates to writing pad for entering information into data processors such as microcomputers. Alphanumeric information is commonly entered into microcomputers by typing on a keyboard, each keystroke is converted into a coded digital signal, such as an ASCII code. In some cases the keys are replaced by an array of key positions of a membrane-type switch. Scanning circuitry is used to scan the rows and columns of key positions to determine which key position is being touched. Writing pads enable a user to enter a sketch into the data processor by "writing" on the surface of the pad. As each point on the sketch is written, the pad senses its location and delivers analog signals corresponding to that location. The analog signals can be converted into digital signals from which the two-coordinate position of the point can be determined. A conventional writing pad is described in European patent application specification 0 107 898 in which a grid of discrete electrical sensing elements are associated with the writing surface, the grid defining an array of discrete locations on the writing surface, the array having a desity of at least 500 locations per square inch (80 locations/cm2) (preferably 5000), the grid being sensitive to writing stimuli received at each location, and digital circuitry connected to the grid for determining the locations at which the stimuli are being received. US patent specification 3 722 369 discloses a writing pad for entering information into a data processor. It addresses the problem of dealing with two input signals in a local region at which stimuli are being received. It exemplifies a capacitive pick-up probe and discloses a writing pad comprising a grid of discrete electrical wires, a writing probe and scanning circuitry. The use of digital circuitry enables a rapid, precise determination of the locations at which stimuli are being received, without the noise associated with analog circuitry; the high density of discrete locations assures that writing can be sensed with high resolution. In view of the high array desity complex and expensive scanning and identifying circuitry is necessary. It is an object of the invention to reduce complexity and size of the scanning and identifying circuitry. An embodiment of a writing pad solving these and associated problems is defined in claim 1 and by the appendant claims. The invention according to claim 1 features circuitry which identifies the upper and lower boundaries along one dimension of the writing surface, of an adaptive local region at which writing stimuli are being received and which extends over more than one of the positions defined by a number of parallel electrical sensing means (conductors) arranged along that dimension. The sensing lines are organized in groups and there are first and second sets of encoders each encoder associated with one of the groups. The first set of encoders is arranged in an order of priority corresponding to the physical order of positions along the one dimension, and the second set of encoders is arranged in an order of priority corresponding to the inverse of the physical order of positions along said one dimension. Prioritizing circuitry is provided for disabling all lower priority encoders within the first set when a higher priority encoder within the first set identifies stimuli received within the positions served by that higher priority encoder, and for disabling all lower priority encoders within the second set when a higher priority encoder within the second set identifies stimuli received within the positions served by that higher priority encoder. The scanning circuitry also identifies the upper and lower boundaries along the second dimension of the local region. Each encoder is capable of providing touch signals to a group encoding circuitry and a switch routes touch signals and binary values to the group encoding circuitry selectively either from the first or second set of encoders. Identifying the upper and lower boundaries of the local region of touching enables substantially instantaneous scanning of the entire writing surface without requiring clocking of the scanning cycles, even where a very large number of lines must be scanned. Having two sets of encoders enables the upper and lower boundaries to be identified while reducing the difficulty of handling local regions of touching which straddle the boundaries between areas served by adjacent encoders. Other advantages and features of the invention will become apparent from the following description of the preferred embodiment and from the claims. We first briefly describe the drawings. Fig. 1 is a writing pad. Fig. 2 is an enlarged, exploded fragmentary isometric view of a representative portion of the pad structure of the pad of Fig. 2. Fig. 3 is an enlarged cross-sectional view, not to scale, of a representative portion of the pad structure taken at 3-3 in Fig. 1. Fig. 4 is a diagram of a portion of the pad writing surface. Fig. 5 is a top view, broken away, of a representative portion of the pad structure with associated circuitry. Figs. 6, 7 are block diagrams of representative portions of the circuitry. Referring to Fig. 1, writing pad 10 has a broad, resilient writing surface 12 which can be written on using a finger or any stylus 14 by simply depressing surface 12 along a line 15 represented by a series of points, for example a point at location 16. Pad 10 is connected to a data processor (not shown) by a cable 18 which carries digital information identifying the locations of the series of points along the line being written. Referring to Fig. 2, writing surface 12 is the upper face of a molded resilient silicone rubber membrane 20 which is the top layer of a pad structure 22. The bottom layer of pad structure 22 is a printed circuit board substrate 24 on which has been printed a series of parallel conductive stripes 26. Each stripe 26 is 125 µm wide and the separation 27 between adjacent stripes is 125 µm Membrane 20 is molded to provide a series of parallel insulative linear spacers 28. Each spacer 28 is 250 µm wide and the separation between adjacent spacers is 250 µm. In the gaps between adjacent spacers are coated parallel conductive stripes 29. Only the ends of stripes 29 appear in Fig. 2. The height 30 of each spacer 28 is 125 µm. When pad structure 22 is assembled, stripes 26 are perpendicular to stripes 29. Spacers 28 keep stripes 26 and stripes 29 electrically separated unless surface 12 is depressed sufficiently to cause electrical contact. Since pressure is equal to force divided by area, a ball point pen with a 500 µm diameter point will produce much more pressure than a palm resting on the surface of the pad. The spacers are arranged to have a resilience such that pressure from a pen point would be sufficient to cause electrical contact but pressure from a palm resting on the pad would not. Thus, the structure 22 defines an array having 5000 contact points per square inch; however, the invention is also useful with any contact point densities of more than 500 per square inch (6,45 cm²). Referring to Fig. 3, when surface 12 is depressed at location 16 by stylus 14, one or more of the stripes 29 are pressed into contact with one or more of the stripes 26 (only one of which appears in Fig. 3). Hereafter stripes 29 and 26 will respectively be referred to as rows and columns. Referring to Fig. 4, the points of contact 30 between rows and columns caused by depressing surface 12 at location 16 all typically lie within a region 32 (indicated by dashed lines). Pad 12 generates digital signals indicating the uppermost and lowermost rows 29, and the leftmost and rightmost columns 26 which are within region 32. Referring to Fig. 5, there are a total of 512 rows 29 and 800 columns 26. At the left edge of pad structure 22 all of the rows are connected to row sensing circuitry 50, while at the right end they are all connected to row powering circuitry 52. Likewise, at the upper and lower edges of structure 22 all columns are connected respectively to column sensing 54 and column powering circuitries 56. The row and column sensing and powering circuitries are all connected to control circuitry 60. The 512 rows are organized into 16 groups, 32 lines per group. (Each row group is labeled R in Fig. 1.) The 800 columns are organized into 25 groups, 32 lines per group. (Each column group is labeled C in Fig. 1.) Only three of the groups of rows and three of the groups of columns are shown in Fig. 5. Each row and each column can be identified by the group to which it belongs and its position within the group, where the groups and the rows and columns within them are all numbered in order along each dimension of the pad. For example, a particular row might be the fourth row down in the eighth group down from the top edge of the pad. Referring to Fig. 6, the rows in each group are connected to an associated row encoding circuit 70 in row sensing circuitry 50. Only one row encoding circuit 70 is shown in detail in Fig. 6. Each column is likewise connected to its own column encoding circuit 72 in column sensing circuitry 54. Only one representative column encoding circuit 72 is indicated in Fig. 6, and its structure is like that of row encoding circuit 70. Each row encoding circuit 70 serves a band of the pad corresponding to the rows connected to it; similarly each column encoding circuit 72 serves a band corresponding to the columns connected to it. Each row encoding circuit 70 includes an upper limit priority encoder 76 and a lower limit priority encoder 78. All 32 rows associated with the encoding circuit are connected to both upper and lower encoders 76, 78. The circuitry within both upper and lower encoders 76, 78 is identical but the rows are connected to the upper encoder in the opposite order from the order of connections for the lower encoder. In each column encoding circuit 72, the priority encoders are called left limit and right limit priority encoders respectively but their functions are analogous to priority encoders 76, 78. All of the priority encoders are of a type like Texas Instruments type SN74LS348 8-line-to-3-line Priority Encoders with 3 State Outputs, except that they encode 32 input lines to 5 output lines. Each lower limit priority encoder 78 is connected by disable lines 80 to carry disable signals to all other lower limit priority encoders serving rows closer to the top of the pad, and is also connected by disable lines 82 to carry disable signals to all other lower limit priority encoders serving rows closer to the top of the pad. Analogous interconnections of the upper limit priority encoders are effected by disable lines 84, 86. Each disable line 82 can itself be disabled (to prevent the delivery of disable signals to the corresponding encoder 78) by a control line 83 from control circuitry 60. Similar disabling interconnections are made among the left limit and right limit priority encoders serving the columns. Thus, the priority encoders are connected to effect orders of priority corresponding to upper, lower, left, and right directions on the pad. Within each priority encoder is circuitry which translates a logical low signal appearing on a particular row or column input into a 5-bit binary value corresponding to the position of that row or column among the 32 rows or columns served by that encoder. For example, if a logical low signal appears on the second uppermost row served by encoder 78, the 5-bit output of the encoder (called lower row # in Fig. 6) is 00010. Each priority encoder circuitry is also arranged so that if logical signals simultaneously appear on more than one of the input rows (or columns), the uppermost one is encoded, the others being ignored. Thus, the rows or columns are connected to each priority encoder to effect orders of priority corresponding to upper, lower, left, and right directions on the pad. Each priority encoder also has a one bit touch output, e.g., the lower touch line 88 coming from encoder 78. The touch line goes high whenever any of the rows (or columns) served by that encoder is high. In each encoding circuit 70, the row # and touch outputs of both encoders 76, 78 are connected through a switch 90 (under control from control circuitry 60) to a conventional 32-to-5 encoder 92. The five-bit row # lines from all switches 90 serving all encoding circuits 70 are connected together, bitwise, and fed to control circuitry 60 over line 94. The touch outputs from all switches 90 are connected to encoder 92. The output of encoder 92 is a 5-bit value (now group #) corresponding to the relative position of the encoding circuit 70 which is delivering a touch output at a given time. For example, if the eighteenth encoding circuit from the top of the pad is providing the touch signal, the output of encoder 92 is 10010. Similar connections exist for the column # and touch outputs of the column encoding circuit 72. Control circuitry 60 is also connected by a drive low line 97 via a row drive circuit 101 to all rows and by a separate drive low line 99 via a column drive circuit 103 to all columns. Referring to Fig. 7, row drive circuit 101 contains a set of gates 105, one for each row. Each gate 105 has its signal input connected to ground, its output to its associated row, and its control input connected to line 97. A similar set of gates 107 is controlled by signals on line 99. Powering circuitries 52, 56 each have parallel 100k ohm resistors 101 each connected between one of the rows and columns and 5 volts DC power supplied from control circuitry 60. With 5 volts connected to powering circuitry 52, control circuitry 60 first drives all columns low by a low signal provided over lines 99 to trigger gates 107 (line 97 remains high). All rows then remain logically high (being powered from circuit 52) except for any rows which are in contact with columns as a result of writing surface 12 being depressed. Several adjacent rows are likely to be in contact with columns at the location 16 where the surface is being depressed (Fig. 4). Each row which is in contact with a column is drawn low. The uppermost one of these rows will be encoded by its upper limit priority encoder into an upper row #. That same encoder will deliver an upper touch signal to its switch 90, and will send disable signals to all upper limit priority encoders which are nearer to the bottom of the pad. Simultaneously, the lowermost one of the rows which is in contact with a column will be encoded by its lower limit priority encoder into a lower row #. That same encoder will deliver a lower touch signal to its switch 90 and will send disable signals to all lower limit priority encoders which are nearer to the top of the pad. As a result the priority encoders 76, 78 essentially instantaneously determine the uppermost and lowermost rows which are in contact with a column. Control circuitry 60 issues a high signal over line 54 to switch 90, which then passes the upper touch signal to encoder 92 and the upper row # to circuitry 60. Encoder 92 then delivers the row group # to circuitry 60. Next control circuitry 60 issues a low signal over line 54 to switch 90 which then passes the lower touch signal to encoder 92 (which delivers the corresponding row group #) and the lower row # to circuitry 60. Next the same process is followed to determine the leftmost and rightmost columns which are in contact with a row. Circuitry 60 supplies 5 volts DC to powering circuitry 56 and drives all rows low by a low signal provided over line 97 to trigger gates 105 (line 99 is set high). The priority encoders essentially instantaneously determine the leftmost and rightmost columns which are in contact, and that information is passed to circuitry 60 by switching between left limit and right limit encoders and encoding of the column group in the same manner as explained above for the rows. The information about the upper, lower, left, and right limits of contact is then delivered over line 18 to a data processor, where the centroid of the location 16 is determined. Circuitry 60 repeats the sequence set forth above with a cycle rate which is rapid enough to accurately track normal speed writing. In the case where pressure from a user's palm at the lower part of the pad occurs simultaneously with pressure from the stylus at the upper part of the pad, the lower boundary of touching may erroneously be sensed at the point where the palm pressure is being applied. Control signals sent over lines 83 can then be used to disable the conveyance of the disable signals to higher ranked lower priority encoders, thus permitting the system to disregard the palm pressure. Thus, the precise points where surface 12 is being depressed are determined almost instantaneously without the need for clocked scanning, notwithstanding that there are a very large number of rows and columns. The speed and accuracy are essentially independent of the number of rows and columns. No analog-to-digital conversion is required.

Claims: A writing pad (10) suitable for entering information into a data processor said pad comprising a writing surface (12) for receiving writing stimuli (14), a two dimensional grid of discrete electrical sensing elements associated with the writing surface (12), the grid defining an array of discrete locations (30) on the writing surface (12), the array having a density of at least 500 locations per square inch (80 locations/cm²), the grid being sensitive to writing stimuli (14) received at each location (30), and scanning circuitry (60) connected to the grid for determining the locations (30) at which writing stimuli (14) are being received, the sensing elements being organized in rows and columns, and the rows and columns being organized into groups, the groups being arranged in a group order corresponding to the physical order of the groups along their corresponding dimension of the grid, characterized by identifying circuitry (50, 52) for identifying the upper and lower boundaries along one of the dimensions of the grid of a region (32) at which writing stimuli (14) are being received, the region (32) encompassing more than one location (30) at which stimuli (14) are being received, first (76) and second (78) sets of encoders, one of the first and one of the second sets of encoders being associated with each group, the first set of encoders (76) having an order of priority corresponding to the group order, and the second set of encoders (78) having an order of priority corresponding to the inverse of the group order, said first set of encoders (76) identifying said upper boundary and said second set of encoders (78) identifying said lower boundary, prioritizing circuitry (80, 82, 84, 86) for disabling all lower priority encoders within the first set (76) when a higher priority encoder within the first set (76) identifies one location (30) at which stimuli (14) are being received within the group associated with the higher priority encoder, and for disabling all lower priority encoders within the second set (78) when a higher priority encoder within the second set (78) identifies one location (30) at which stimuli (14) are being received within the group associated with the higher priority encoder. The writing pad (10) of claim 1 characterized by identifying circuitry (54, 56) for identifying the upper and lower boundaries along the other one of dimensions of the grid of said local region (32). The writing pad (10) of claim 1 or 2 wherein each said one of the first and one of the second set of encoders forms an encoding circuit (70) for providing a binary signal indicative of said region (32) along one of the dimensions of the grid. The writing pad (10) of claim 1 or 2 characterized in that said first set of encoders (76) includes a means for providing a touch signal from the highest priority encoder when it identifies a position (30) at which stimuli (14) are being received, and said second set of encoders (78) includes a means (88) for providing a touch signal from the highest priority encoder when it identifies the position (30) at which stimuli (14) are being received, said scanning circuitry (60) comprising group encoding circuitry (90, 92) connected to receive the touch signal from the first set of encoders (76) and to represent the touch signal by a binary signal indicative of the position of the first encoder (76) in its group priority and connected to receive the touch signal from the second set of encoders (78) and to represent the touch signal by a binary signal indicative of the position of the second encoder (78) in its group priority.

Inventors: HO, SHU-KUANG, MAINEMER, CARLOS I., WANG, AN, DR.
Applicants: WANG LABORATORIES INC.
Application year: 1986
Main classification: G06K11
IPC codes: G06F3