APPARATUS FOR DETECTING A LOCATION OF AN OBJECT ON A TABLET

Abstract: A graphics tablet (100) is presented which has an x-y grid of wire traces (141 - 164; 171 - 194) embedded on it. Drive wires (x1 - x8; y1 - y8) are coupled to the trace wires in both the x-direction and the y-direction. When a stylus (198) is placed in contact with the graphics tablet (100), the location of a sector of the graphics tablet where the stylus (198) contacts the graphics tablet may be determined by sequentially placing a signal on each drive wire (x1 - x8; y1 - y8) and measuring the strength of the signal received by the stylus. The closer the stylus is to a particular trace, the stronger the signal which is received by the stylus from the drive wire coupled to that trace. The identity of a plurality of drive wires in the x-­ direction and a plurality of wires in the y-direction with the strongest received signal can be used to determine a unique address for the location of the sector of the graphics tablet where the stylus contacts the graphics tablet.

Description: The present invention relates to an apparatus for detecting a location of an object on a tablet in accordance with the precharacterizing part of claim 1. Such an apparatus is known from US-A-3 999 012. A prior art graphics tablet might include a platen which contains an X-Y grid of wires on a pc board. For instance, a graphics tablet model number HP9111A made by Hewlett-Packard Company of Palo Alto, California has 56 wires in the X-direction and 46 wires in the Y-direction. Typically in the prior art each trace has required its own wire driving circuitry. This circuitry adds significant cost to the manufacture and design of a graphics tablet. The apparatus known from US-A-3 999 012 has a reduced number of X- and Y-drivers. However, the group arrangement of X- and Y-wires effects a relatively complicated wiring pattern on the tablet. The US-A-3 975 592 discloses means for determining the proximity of a probe relative to a plurality of conductors. It is an object of the invention to reduce the cost of the drivers circuitry used to energize the row- and column wire traces on the graphics tablet and to achieve a simple arrangement of these row and column wire traces on the tablet. The object is solved in accordance with the characterizing features of claim 1. The dependent claims characterize advantageous developments thereof. The invention will be explained hereafter in detail and described with reference to the embodiments shown in the drawing. The features apparent from the specification and the drawing may be used in other embodiments of the invention either individually or in any desired combination thereof. In the drawing: Figure 1 shows a graphics tablet with an X-Y grid of row- and column wires embedded thereon in accordance with a preferred embodiment of the present invention. Figure 2 is an enlarged diagram of a portion of the grid of row- and column wires shown in Figure 1. Figure 3 shows another graphics tablet with an X-Y grid of row- and column wires embedded thereon in accordance with another embodiment of the present invention. Figure 1 shows an X-Y grid of row- and column wires organized on a graphics tablet 100. The X-Y grid of the row- and column wires includes row wires 141-164 used to determine locations in the X-direction and column wires 171-194 used to determine locations in the Y-direction. Also on the graphics tablet 100, row driver lines X1 to X8 are coupled to driver circuitry 197 at driver line ends 105. Column driver lines Y1 to Y8 are coupled to driver circuitry 197 at driver line ends 106. The column wires 171-194 are coupled to the column driver lines Y1-Y8 in groups and in permuted order as shown. Similarly, the row wires 141-164 are coupled to the row driver lines X1-X8 in groups and in permuted order as shown. The following table lists the row wires 141-164 and indicates which row driver line from the driver lines X1-X8 is coupled to each row wire. Row-wire Row driver line connected thereto 141 X1 142 X2 143 X3 144 X4 145 X5 146 X6 147 X7 148 X8 149 X3 150 X2 151 X5 152 X4 153 X7 154 X6 155 X3 156 X8 157 X5 158 X4 159 X1 160 X2 161 X7 162 X8 163 X5 164 X6 Similarly the following table 2 lists the column wires 171-194 and indicates which column driver line from driver lines Y1-Y8 is coupled to each column wire. Column wire Column driver line connected thereto 171 Y1 172 Y2 173 Y3 174 Y4 175 Y5 176 Y6 177 Y7 178 Y8 179 Y3 180 Y2 181 Y5 182 Y4 183 Y7 184 Y6 185 Y3 186 Y8 187 Y5 188 Y4 189 Y1 190 Y2 191 Y7 192 Y8 193 Y5 194 Y6 The X-Y grid of row and column wires interfaces to driver circuitry 197 by means of ends 105 of row driver lines X1-X8 and by means of ends 106 of column lines Y1-Y8. Driver circuitry 197 is coupled to a microprocessor 196. When a stylus 198 or other signal detecting device is placed on the graphics tablet a coarse location can be determined by sequentially placing a signal on each row driver line X1-X8 and measuring the strength of the signal received by stylus 198. Sensing circuitry 199 coupled to stylus 198 measures the relative strength of the signals and gives this information to microprocessor. For instance, the three driver lines for the X-direction (i.e., row driver lines X1-X8) from which stylus 198 receives the strongest signals are used to determine an address in the X-direction for the sector location of stylus 198. Likewise, the three column lines for the Y-direction (i.e. column driver lines Y1-Y8) from which stylus 198 receives the strongest signal are used to determine an address in the Y-direction for the sector location of stylus 198. A section 131 of array 100 is shown in Figure 2 for further explanation of how addresses are derived. In Figure 2, row wires 157, 158, 159 and 160 for the X-direction and column wires 179, 180, 181 and 182 for the Y-direction are shown. From Table 1, row wire 157 is coupled to row driver line X5, row wire 158 is coupled to row driver line X4, row wire 159 is coupled to row driver line X1, and row wire 160 is coupled to row driver line X2. From Table 2, column wire 179 is coupled to column driver line Y3, column wire 180 is coupled to column driver line Y2, column wire 181 is coupled to column driver line Y5, and column wire 182 is coupled to column driver line Y4. The strength of the signals coupled from row wires 141-164 and column wires 171-194 to stylus 198 can be used to determine which sector stylus 198 is placed in. For instance, if stylus 198 is placed in a sector 201, for determination of the X-direction, stylus 198 would be closest to row wire 158, second closest to row wire 159 and third closest to row wire 157. Therefore, for row driver lines for the X-direction stylus 198 would receive the strongest signal from row driver line X4, the second strongest signal from row driver line X1 and the third strongest signal from row driver line X5. Thus, preserving the order of strongest to third strongest, the address for sector 201 in the X-direction would be X4, X1, X5, or X(415). Likewise, when stylus 198 is in sector 201, for determination of the Y-direction, stylus 198 would be closest to column wire 181, second closest to column wire 180 and third closest to column wire 182. Therefore, for column driver lines in the Y-direction stylus 198 would receive the strongest signal from the column driver line Y5, the second strongest signal from column driver line Y2 and the third strongest signal from column driver line Y4. Thus again preserving the order of strongest to third strongest, the address for sector 201 in the Y-direction would be Y5, Y2, Y4, or Y(524). The address for sector 201 may thus be written X(415), Y(524). Similarly, the addresses for a sector 202, a sector 203 and a sector 204 may be calculated. The address for sector 202 is X(142), Y(524); the address for sector 203 is X(415), Y(253); and the address for sector 204 is X(142), Y(253). Care must be taken in selecting the ordering of the coupling of the driver lines to the traces to insure each sector on a board has a unique address. Depending upon the size of the graphics board and the number of driver lines used, it may be desirable to calculate a unique address by using other than three driver lines for each direction (i.e., three row driver lines for the X-direction and three column driver lines for the Y-direction). For instance, the nearest two wires or the nearest four wires may be used to calculate a unique address for each sector in each direction. Also, it would be possible to originate a signal from stylus 198 and detect signals on each of the driver lines. A relatively strong signal received by a particular driver line would indicate that stylus 198 contacts the graphics board relatively close to a trace wire coupled to that driver wire. Additionally, traces may be ordered in such a way as to avoid erroneous data. For instance, if stylus 198 is in sector 201 but very close to a border 210 between sector 201 and 202, then the unique address determined in the X-direction should be X(415). However, noise in the system might lead to an erroneous determination that the address is X(412). Similarly, if stylus 198 is in sector 202 but very close to border 210, then noise in the system may erroneously lead to determination the address in the X-direction is X(145) rather than the correct X(142). By proper ordering of the traces so that addresses X(412) and X(145) do not uniquely address another sector, (as has been done in the preferred embodiment), these addresses, although erroneously determined, may still be used to reference the location where stylus 198 is located. The above discussion has centered on locating a sector in which stylus 198 is located. Once the sector is located, if a more precise location needs to be determined, this can be done using a simple centroid calculation based on the relative strength of signals received from the three nearest traces. Figure 3 shows a graphics tablet array 400 using eight row driver lines for the X-direction and eight column driver lines for the Y-direction. There are 56 row wires for determining location of a stylus in the Y-direction. Outline section 401 shows the area within which the graphics tablet array 400 is divided into sectors, each sector having a unique address.

Claims: An apparatus for detecting a location of an object on a tablet (100), the apparatus comprising: a plurality of row wires (141-164) laid out on the tablet in one dimension in groups, whereby row wires from different groups are connected together and then connected to row driver lines (X1-X8); a plurality of row drivers (197) which are connected to the row driver lines (X1-X8); first row detecting means (189) coupled to the said object for detecting a row driver line connected to a row wire that is closest to the object; second row detecting means (199) for detecting the group to which the row wire closest to the object belongs; and row address determining means (196) for determining an address of the location of the object based on the identities of the detected row driver lines and on the detected group, characterized in that I the order of the row driver lines respectively connected to the consecutive row wires in a group is permuted and thus identifies each group; II the first row detecting means detects in addition to the row driver line of the closest row wire the row driver line of the second and third closest row wires; III the second row detecting means includes means for identifying the group containing said closest row wires, the address of each group being defined by the order and identities of the first, second and third closest row driver lines so as to uniquely specify one group of row wires only. The apparatus according to claim 1, characterized by additionally comprising a plurality of column wires (171-194) laid out on the tablet (100) in groups perpendicularly to the plurality of row wires (141-164), whereby column wires from different groups are connected together and then connected to column driver lines (Y1-Y8); a plurality of column drivers (197) which are connected to the column driver lines (Y1-Y8), wherein the order of the column driver lines (Y1-Y8) are respectively connected to the consecutive column wires in a group is permuted and thus identifies each group; column detecting means (198) coupled to the object for detecting a column driver line connected to the column wire that is closest to the object and additionally for detecting the column driver lines of the second and third closest column wires; and second column detecting means (199) for identifying the group containing said closest column wires and the address of the location of the object based on the identities of the detected driver lines, the address of each group being defined by the order and the identities of the first, second and third closest column driver lines so as to uniquely specify one group of column wires only. The apparatus according to claim 2, characterized by additionally comprising signal generation means for generating a signal on each of the plurality of row driver lines (X1-X8) and on each of the plurality of column driver lines (X1-Y8), wherein said first row detecting means and said first column detecting means are detecting the relative strength of the signals generated on each of the plurality of row driver lines (X1-X8) and on each of the plurality of column driver lines (Y1-Y8). The apparatus according to claim 3 characterized by additionally comprising locating means (196) for locating the object based on the relative strength of signals generated by the signal generation means on at least two row driver lines and on at least two column driver lines and detected by the first and second row and column detecting means.

Inventors: BERKE, W. MIKE, MALZBENDER, THOMAS
Applicants: HEWLETT-PACKARD COMPANY
Application year: 1986
Main classification: G06K11
IPC codes: G06F3