Electrostatic input device
An electrostatic input device includes electrostatic sensor electrodes, a measurement circuit that outputs a measurement value, a control unit that determines whether a state is a proximity state in which the indication body is close to the sensor electrodes, and a storage unit that stores as a reference value a measurement value in a state in which the indication body is not close to the sensor electrodes, wherein the control unit determines whether a state is a proximity state based on a first difference value obtained by subtracting the reference value from a measurement value, calculates a sum difference value obtained by summing up the first difference values, and when a state in which a fluctuation amount of the sum difference value is smaller than a predetermined value continues for a predetermined time or longer after the sum difference value decreases in the proximity state, updates the reference value.
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.