Optical scanning device and method of adjusting optical scanning device

An optical scanning device comprising:

• a mirror part having a mirror surface configured to reflect light N (N>3) support cantilevers supporting the mirror part swingably;
• and
• N drive cantilevers respectively connected to the N support cantilevers, wherein the N drive cantilevers are arranged to surround the mirror part, an end of both ends of each of the N drive cantilevers that is not connected to the support cantilever is fixed, and each of the N drive cantilevers has a shape bent one or more times,
• the optical scanning device further comprising:
• a plurality of driving piezoelectric elements secured on the N drive cantilevers;
• and
• a power supply unit configured to apply AC voltage to the piezoelectric elements, wherein the mirror part precesses by setting a frequency of AC voltage applied to each of the piezoelectric elements to a common value and setting a phase of AC voltage applied to each of the piezoelectric elements to a value determined according to a position of the piezoelectric element,
• the N support cantilevers are arranged in (360°/N) rotational symmetry with respect to a center axis of the mirror part,
• the mirror part has a first natural frequency mode of being rotationally displaced around a first axis and a second natural frequency mode of being rotationally displaced around a second axis, the first axis and the second axis being parallel to the mirror surface, a direction of the first axis being a direction of a straight line connecting a center of the mirror part with a connection portion between the mirror part and one of the N support cantilevers, the second axis being orthogonal to the first axis,
• the power supply unit applies AC voltage at an intermediate frequency between a resonance frequency in the first natural frequency mode and a resonance frequency in the second natural frequency mode,
• an amplitude and an initial phase of the AC voltage are adjustable, and
• the power supply unit includes N drive power supplies each applying AC voltage to a plurality of piezoelectric elements on a corresponding drive cantilever,
• the optical scanning device further comprising a control unit configured to, in adjustment of the initial phase of the AC voltage, select one drive cantilever from among the N drive cantilevers, fix the amplitude and the initial phase of AC voltage applied to a plurality of piezoelectric elements on one or more drive cantilevers other than the selected drive cantilever, and fix the amplitude of AC voltage applied to a plurality of piezoelectric elements on the selected drive cantilever, and change the initial phase to determine the initial phase at which rotation linearity error is smallest as an adjustment value of the initial phase of AC voltage applied to a plurality of piezoelectric elements on the selected drive cantilever,
• wherein the rotation linearity error is a quantity that represents a deviation from linearity of all-round rotational displacement of the mirror part, and the all-round rotational displacement of the mirror part is a displacement of the mirror part such that the center axis of the mirror part makes a turn while a deflection angle of the mirror part is kept constant.

An optical scanning device comprising:

• a mirror part having a mirror surface configured to reflect light;
• N (N>3) support cantilevers supporting the mirror part swingably;
• and
• N drive cantilevers respectively connected to the N support cantilevers,
• wherein the N drive cantilevers are arranged to surround the mirror part, an end of both ends of each of the N drive cantilevers that is not connected to the support cantilever is fixed, and each of the N drive cantilevers has a shape bent one or more times,
• the optical scanning device further comprising:
• a plurality of driving piezoelectric elements secured on the N drive cantilevers:
• and
• a power supply unit configured to apply AC voltage to the piezoelectric elements,
• wherein the mirror part precesses by setting a frequency of AC voltage applied to each of the piezoelectric elements to a common value and setting a phase of AC voltage applied to each of the piezoelectric elements to a value determined according to a position of the piezoelectric element,
• the N support cantilevers are arranged in (360°/N) rotational symmetry with respect to a center axis of the mirror part,
• the mirror part has a first natural frequency mode of being rotationally displaced around a first axis and a second natural frequency mode of being rotationally displaced around a second axis, the first axis and the second axis being parallel to the mirror surface, a direction of the first axis being a direction of a straight line connecting a center of the mirror part with a connection portion between the mirror part and one of the N support cantilevers, the second axis being orthogonal to the first axis,
• the power supply unit applies AC voltage at an intermediate frequency between a resonance frequency in the first natural frequency mode and a resonance frequency in the second natural frequency mode,
• an amplitude and an initial phase of the AC voltage are adjustable, and
• the power supply unit includes N drive power supplies each applying AC voltage to a plurality of piezoelectric of piezoelectric elements on a corresponding drive cantilever,
• the optical scanning device further comprising a control unit configured to, in adjustment of the amplitude of AC voltage, select one drive cantilever from among the N drive cantilevers, fix the amplitude and the initial phase of AC voltage applied to a plurality of piezoelectric elements on one or more drive cantilevers other than the selected drive cantilever, fix the initial phase of AC voltage applied to a plurality of piezoelectric elements on the selected drive cantilever, and change the amplitude to determine the amplitude at which rotation linearity error is smallest as an adjustment value of amplitude of AC voltage applied to a plurality of piezoelectric elements on the selected drive cantilever,
• wherein the rotation linearity error is a quantity that represents a deviation from linearity of all-round rotational displacement of the mirror part, and the all-round rotational displacement of the mirror part is a displacement of the mirror part such that the center axis of the mirror part makes a turn while a deflection angle of the mirror part is kept constant.

An optical scanning device comprising:

• a mirror part having a mirror surface configured to reflect light;
• N (N>3) support cantilevers supporting the mirror part swingably;
• and
• N drive cantilevers respectively connected to the N support cantilevers,
• wherein the N drive cantilevers are arranged to surround the mirror part, an end of both ends of each of the N drive cantilevers that is not connected to the support cantilever is fixed, and each of the N drive cantilevers has a shape bent one or more times,
• the optical scanning device further comprising:
• a plurality of driving piezoelectric elements secured on the N drive cantilevers:
• and
• a power supply unit configured to apply AC voltage to the piezoelectric elements,
• wherein the mirror part precesses by setting a frequency of AC voltage applied to each of the piezoelectric elements to a common value and setting a phase of AC voltage applied to each of the piezoelectric elements to a value determined according to a position of the piezoelectric element,
• the N support cantilevers are arranged in (360°/N) rotational symmetry with respect to a center axis of the mirror part,
• the mirror part has a first natural frequency mode of being rotationally displaced around a first axis and a second natural frequency mode of being rotationally displaced around a second axis, the first axis and the second axis being parallel to the mirror surface, a direction of the first axis being a direction of a straight line connecting a center of the mirror part with a connection portion between the mirror part and one of the N support cantilevers, the second axis being orthogonal to the first axis,
• the power supply unit applies AC voltage at an intermediate frequency between a resonance frequency in the first natural frequency mode and a resonance frequency in the second natural frequency mode,
• an amplitude and an initial phase of the AC voltage are adjustable, wherein
• N=4,
• four drive cantilevers are ordered clockwise or counterclockwise,
• four support cantilevers are arranged in 90° rotational symmetry with respect to the center axis of the mirror part, four drive cantilevers are arranged in 90° rotational symmetry with respect to the center axis of the mirror part, and, of portions that constitute each of the four drive cantilevers, each of a plurality of circumferential portions extending in a same direction as a circumferential direction of the mirror part has two piezoelectric elements,
• the power supply unit includes
• a first drive power supply configured to output a first AC voltage having a first initial phase and a first amplitude and a second AC voltage having a phase different from the first AC voltage by 180 degrees, and
• a second drive power supply configured to output a third AC voltage having a second initial phase and a second amplitude and a fourth AC voltage having a phase from the third AC voltage by 180 degrees,
• the first drive power supply applies the first AC voltage to a first piezoelectric element near the support cantilever, of a plurality of piezoelectric elements arranged on the first drive cantilever, and applies the first AC voltage or the second AC voltage to other piezoelectric elements arranged on the first drive cantilever, applies the second AC voltage to a second piezoelectric element near the support cantilever, of a plurality of piezoelectric elements arranged on the third drive cantilever, and applies the first AC voltage or the second AC voltage to other piezoelectric elements arranged on the third drive cantilever, and
• the second drive power supply applies the third AC voltage to a third piezoelectric element near the support cantilever, of a plurality of piezoelectric elements arranged on the second drive cantilever, applies the third AC voltage or the fourth AC voltage to other piezoelectric elements arranged on the second drive cantilever, applies the fourth AC voltage to a fourth piezoelectric element near the support cantilever, of a plurality of piezoelectric elements arranged on the fourth drive cantilever, and applies the third AC voltage or the fourth AC voltage to other piezoelectric elements arranged on the fourth drive cantilever.