Method for determining incline angle of electromagnetic pointer
A method for determining an incline angle of an electromagnetic pointer is provided. The electromagnetic pointer is positioned on or above a digitizer which has a plurality of loop antennas. The method comprises steps of: locating a peak-value loop antenna which has a maximum inductive signal value; scanning plural loop antennas that are near to the peak-value loop antenna so as to obtain a signal distribution; simulating at least two signal curves by using signal values sensed by the peak-value loop antenna and the neighboring loop antennas; calculating a rate of change between every two signal curves; and determining an incline angle of the electromagnetic pointer by looking up a conversion table with the calculated rate of change. The present invention only needs to scan five to seven loop antennas to determine the incline angle, thereby increasing the efficiency of incline angle determination.
1. A method for determining an incline angle of an electromagnetic pointer, the electromagnetic pointer being positioned on or above a digitizer, the digitizer having a plurality of loop antennas, said method comprising steps of:
A. locating a peak-value loop antenna which has a maximum inductive signal value;
B. scanning plural loop antennas that are near to the peak-value loop antenna and obtaining seven inductive signal values from seven loop antennas among the peak-value loop antenna and the neighboring loop antennas;
C. simulating one signal curve with a cubic equation in one variable for every four adjacent points taken from the seven signal values, in which highest-ordered parameters for four signal curves obtained from the simulation respectively are A −2 , A −1 , A 0 , and A 1 in order;
D. defining following variables by calculating variations among the signal curves:
Index1= A 0 −A −1
Delta L=A 0 −A −2
Delta R=A 1 −A −1
Index2=Delta L −Delta R;
E. determining an inductive distance between the electromagnetic pointer and the digitizer according to values of DeltaL and DeltaR; and
F. determining an incline angle of the electromagnetic pointer by using values of Index1 and Index2 to look up an incline angle conversion table.
2. The method according to claim 1 , wherein in Step A, the peak-value loop antenna having the maximum inductive signal value is determined when a global scan is carried on.
3. The method according to claim 1 , wherein in Step B, the inductive signal values of the neighboring loop antennas are acquired when a local scan is carried on.
4. The method according to claim 1 , wherein the highest-ordered parameters A −2 , A −1 , A 0 , and A 1 are normalized in Step C and then in Step D, the variations are calculated.
5. The method according to claim 1 , wherein in Step E, the incline angle conversion table varies with different inductive distances.
6. The method according to claim 1 , wherein in Step F, the incline angle conversion table is a table on which the incline angle and position percentage are in comparison with Index1 and Index2.
7. The method according to claim 1 , wherein Step F comprises steps of:
F1. determining whether a coordinate of the electromagnetic pointer falls into a range of the peak-value loop antenna;
F2. using a value of Index2 to look up the incline angle conversion table so as to obtain a corresponding incline angle of the electromagnetic pointer when the coordinate of the electromagnetic pointer falls into the range of the peak-value loop antenna; and
F3. using a value of Index1 to look up the incline angle conversion table so as to obtain the corresponding incline angle of the electromagnetic pointer when the coordinate of the electromagnetic pointer does not fall into the range of the peak-value loop antenna.
8. The method according to claim 7 , wherein whether the coordinate of the electromagnetic pointer falls into the range of the peak-value loop antenna or not is determined according to the values of Index1 and Index2.