MEMS actuator, MEMS actuator drive method, and MEMS actuator control program

A MEMS actuator, comprising:

• a base portion;
• a movable portion supported so as to be elastically displaceable with respect to the base portion;
• a first fixed comb electrode including a plurality of first comb fingers and provided to the base portion;
• a first movable comb electrode that includes a plurality of second comb fingers and drives the movable portion by an electrostatic force generated between the first fixed comb electrode and the first movable comb electrode, the plurality of first comb fingers and the plurality of second comb fingers being alternately arranged;
• a second fixed comb electrode including a plurality of third comb fingers and provided to the base portion;
• a second movable comb electrode including a plurality of fourth comb fingers, the plurality of third comb fingers and the plurality of fourth comb fingers being alternately arranged;
• a drive circuit that applies a drive voltage having a time waveform periodically repeating rising and falling between the first fixed comb electrode and the first movable comb electrode;
• and
• a timing detection circuit that applies a voltage including a period to be a constant voltage excluding 0 V between the second fixed comb electrode and the second movable comb electrode, generates a capacitance derivative signal indicating a derivative value of a capacitance between the second fixed comb electrode and the second movable comb electrode by converting a current signal, which is output from the second fixed comb electrode or the second movable comb electrode within the period due to a change in the capacitance, into a voltage signal, and detects a timing when the capacitance derivative signal reaches a threshold value,
• wherein the drive circuit controls a timing of the falling or a timing of the rising of the drive voltage based on the capacitance derivative signal such that a relationship between the timing detected by the timing detection circuit and the timing of the falling to be is kept constant in real time, regardless of a fluctuation in a resonance frequency of the movable portion.

A MEMS actuator, comprising:

• a base portion;
• a movable portion supported so as to be elastically displaceable with respect to the base portion;
• a fixed comb electrode including a plurality of first comb fingers and provided to the base portion;
• a movable comb electrode that includes a plurality of second comb fingers and drives the movable portion by an electrostatic force generated between the fixed comb electrode and the movable comb electrode, the plurality of first comb fingers and the plurality of second comb fingers being alternately arranged;
• a drive circuit that applies a drive voltage having a time waveform, which periodically repeats rising and falling and includes a period to be a constant voltage after the rising and before the falling, between the fixed comb electrode and the movable comb electrode;
• and
• a timing detection circuit that generates a capacitance derivative signal indicating a derivative value of a capacitance between the fixed comb electrode and the movable comb electrode by converting a current signal, which is output from the fixed comb electrode or the movable comb electrode within the period due to a change in the capacitance, into a voltage signal and detects a timing when the capacitance derivative signal reaches a threshold value,
• wherein the drive circuit controls a relationship between the timing detected by the timing detection circuit and a timing of the falling to be constant,
• wherein the movable portion is a slide type.

A method for driving a MEMS actuator including a base portion, a movable portion supported so as to be elastically displaceable with respect to the base portion, a fixed comb electrode including a plurality of first comb fingers and provided to the base portion, and a movable comb electrode including a plurality of second comb fingers and driving the movable portion by an electrostatic force generated between the fixed comb electrode and the movable comb electrode, the plurality of first comb fingers and the plurality of second comb fingers being alternately arranged, the MEMS actuator drive method comprising:

• a drive step for applying a drive voltage having a time waveform, which periodically repeats rising and falling and includes a period to be a constant voltage after the rising and before the falling, between the fixed comb electrode and the movable comb electrode,
• wherein, in the drive step, a capacitance derivative signal indicating a derivative value of a capacitance between the fixed comb electrode and the movable comb electrode is generated by converting a current signal, which is output from the fixed comb electrode or the movable comb electrode within the period due to a change in the capacitance, into a voltage signal, a timing when the capacitance derivative signal reaches a threshold value is detected, and a timing of the falling or a timing of the rising of the drive voltage is controlled based on the capacitance derivative signal such that a relationship between the timing when the capacitance derivative signal reaches the threshold value is detected and the timing of the falling is controlled to be constant in real time, regardless of a fluctuation in a resonance frequency of the movable portion.

A method for driving a MEMS actuator including a base portion, a movable portion supported so as to be elastically displaceable with respect to the base portion, a first fixed comb electrode including a plurality of first comb fingers and provided to the base portion, a first movable comb electrode including a plurality of second comb fingers and driving the movable portion by an electrostatic force generated between the first fixed comb electrode and the first movable comb electrode, the plurality of first comb fingers and the plurality of second comb fingers being alternately arranged, a second fixed comb electrode including a plurality of third comb fingers and provided to the base portion, and a second movable comb electrode including a plurality of fourth comb fingers, the plurality of third comb fingers and the plurality of fourth comb fingers being alternately arranged, the MEMS actuator drive method comprising:

• a drive step for applying a drive voltage having a time waveform periodically repeating rising and falling between the first fixed comb electrode and the first movable comb electrode,
• wherein, in the drive step, a voltage including a period to be a constant voltage excluding 0 V is applied between the second fixed comb electrode and the second movable comb electrode, a capacitance derivative signal indicating a derivative value of a capacitance between the second fixed comb electrode and the second movable comb electrode is generated by converting a current signal, which is output from the second fixed comb electrode or the second movable comb electrode within the period due to a change in the capacitance, into a voltage signal, a timing when the capacitance derivative signal reaches a threshold value is detected, and a timing of the falling or a timing of the rising of the drive voltage is controlled based on the capacitance derivative signal such that a relationship between the timing when the capacitance derivative signal reaches the threshold value is detected and the timing of the falling is controlled to be constant in real time, regardless of a fluctuation in a resonance frequency of the movable portion.