Electrostatic input device

1 . An electrostatic input device comprising:

a plurality of electrostatic sensor electrodes;

a measurement circuit configured to output a plurality of measurement values based on a capacitance between each of the plurality of electrostatic sensor electrodes and an indication body at a predetermined interval;

a processor configured to determine, based on the plurality of measurement values, a proximity state in which the indication body is in proximity to the plurality of electrostatic sensor electrodes; and

a memory configured to store, as a reference value, a predetermined measurement value output from the measurement circuit, the reference value corresponding to a non-proximity state in which the indication body is not in proximity to the plurality of electrostatic sensor electrodes,

wherein the processor is further configured to:

determine the proximity state based on a plurality of first difference values obtained by subtracting the reference value from, each of the plurality of measurement values;

calculate a plurality of sum difference values obtained by summing up the plurality of first difference values at the predetermined interval;

determine, in the proximity state, a first state in which a current sum difference value of the plurality of sum difference values decreases more than a first previous sum difference value of the plurality of sum difference values;

determine, in the proximity state, whether a fluctuation amount of the plurality of sum difference values is smaller than a predetermined value after the processor determines that the current sum difference value decreases more than the first previous sum difference value;

determine, in the proximity state, whether a second state, in which the fluctuation amount of the plurality of sum difference values is smaller than the predetermined value, continues for a predetermined time or more;

update the reference value to an updated reference value under conditions below:

the processor determines, in the proximity state, the first state at a first time; and

the processor determines that the second state continues for the predetermined time or more from the first time; and

determine the proximity state based on a plurality of second difference values obtained by subtracting the updated reference value from each of the plurality of measurement values.

2 . The electrostatic input device according to claim 1 ,

wherein the processor is further configured to:

cause the memory to store a highest value of the plurality of sum difference values as a maximum sum difference value; and

determine the first state under a condition in which a third difference value, obtained by subtracting the current sum difference value from the maximum sum difference value, is larger than a decrease threshold value.

3 . The electrostatic input device according to claim 2 ,

wherein the processor is further configured to cause the memory to store one of the plurality of sum difference values in the proximity state as a low temperature sum difference value under a condition below:

a temperature around the plurality of electrostatic sensor electrodes is lower than a temperature threshold value, and

the decrease threshold value is obtained by multiplying the low temperature sum difference value by a first constant.

4 . The electrostatic input device according to claim 3 ,

wherein the processor is further configured to:

determine the proximity state under a condition below:

any of the plurality of first difference values is larger than a proximity threshold value; and

determine the non-proximity state under a condition below:

each of the plurality of first difference values is smaller than a non-proximity threshold, value;

transition to a proximity monitoring state under conditions below:

the processor determines, in the proximity state, the first state at the first time; and

the processor determines that any of the plurality of first difference values is larger than the non-proximity threshold value from the first time;

transition to a non-proximity monitoring state under conditions below:

the processor determines, in the proximity state, the first state at the first time; and

the processor determines that each of the plurality of first difference values is lower than the non-proximity threshold value from the first time; and

determine, in the proximity monitoring state or in the non-proximity monitoring state, the proximity state under a condition in which an increase amount between the current sum difference value of the plurality of sum difference values and a second previous sum difference value of the plurality of sum difference values is larger than a predetermined increase amount.

5 . The electrostatic input device according to claim 4 ,

wherein the processor is further configured to determine that the increase amount exists under a condition in which the third difference value is smaller than an increase threshold value.

6 . The electrostatic input device according to claim 5 ,

wherein the increase threshold value is obtained by multiplying the low temperature sum difference value by a second constant.

7 . The electrostatic input device according to claim 5 ,

wherein the processor is further configured to, in the proximity monitoring state, transition to the proximity state under a condition in which the current sum difference value of the plurality of sum difference values is changed from a third previous sum difference value of the plurality of sum difference values.

8 . The electrostatic input device according to claim 7 ,

wherein the processor is further configured to:

calculate a fourth difference value by subtracting the low temperature sum difference value from one of the plurality of sum difference values; and

transition to the proximity state under conditions below:

the fourth difference value is larger than a positive first change constant; or

the fourth difference value is smaller than a negative second change constant.

9 . The electrostatic input device according to claim 8 ,

wherein the processor is configured to update the reference value to the updated reference value under further conditions below:

the non-proximity monitoring state continues longer than a first update time; or

the proximity monitoring state continues longer than a second update time, and

the first update time is shorter than the second update time.

10 . The electrostatic input device according to claim 8 ,

wherein the processor is further configured to, in the non-proximity monitoring state, transition to the non-proximity state without updating the reference value to the updated reference value under a condition below:

one of the plurality of sum difference values is smaller than a predetermined minimum threshold value.

11 . The electrostatic input device further comprising:

a temperature sensor configured to measure a temperature around the plurality of electrostatic sensor electrodes,

wherein the processor is configured to perform the processes defined in claim 1 under conditions below:

the processor determines the proximity state; and

the temperature around the plurality of electrostatic sensor electrodes is lower than a temperature threshold value.

12 . The electrostatic input device according to claim 1

wherein the processor is further configured to:

determine whether the reference value is smaller than a corresponding reference value in a predetermined temperature condition lower than a regular temperature condition; and

perform the processes defined in claim 1 under conditions below:

the processor determines the proximity state; and

the processor determines that the reference value is smaller than the corresponding reference value in the predetermined temperature condition.

13 . An electrostatic input device comprising:

an electrostatic sensor electrode;

a measurement circuit configured to output a plurality of measurement values based on a capacitance between the electrostatic sensor electrode and an indication body at a predetermined interval;

a processor configured to determine, based on the plurality of measurement values, a proximity state in which the indication body is in proximity to the electrostatic sensor electrode; and

a memory configured to store, as a reference value, a predetermined measurement value output from the measurement circuit, the reference value corresponding to a non-proximity state in which the indication body is not in proximity to the electrostatic sensor electrode,

wherein the processor is further configured to:

determine the proximity state based on a plurality of first difference values obtained by subtracting the reference value from each of the plurality of measurement values;

determine, in the proximity state, a first state in which a current first difference value of the plurality of first difference values decreases more than a previous first difference value of the plurality of first difference values;

determine, in the proximity state, whether a fluctuation amount of the plurality of first difference values is smaller than a predetermined value after the processor determines that the current first difference value decreases more than the previous first difference value;

determine, in the proximity state, whether a second state, in which the fluctuation amount of the plurality of first difference values is smaller than the predetermined value, continues for a predetermined time or more;

update the reference value to an updated reference value under conditions below:

the processor determines, in the proximity state, the first state at a first time; and

the processor determines that the second state continues for the predetermined time or more from the first time; and

determine the proximity state based on a plurality of second difference values obtained by subtracting the updated reference value from each of the plurality of measurement values.