Drive method for ultrasonic motor providing enhanced stability of rotation

Claim 1

A method of driving an ultrasonic motor comprising a vibration body formed of a piezoelectric body and an elastic body and a rotary body which is disposed in contact with said vibration body, the vibration body being driven to vibrate by an alternating drive voltage which is applied to said piezoelectric body for thereby rotating the rotary body by a frictional force, the method comprising successive steps of: (a) sweeping a drive frequency of said vibration body downward from a high end of a predetermined frequency sweep range, said sweep range including at least a frequency range extending between an antiresonance frequency of said vibration body and a highest resonance frequency of said vibration body with respect to a hysteresis loop exhibited by a resonance frequency characteristic of said vibration body; (b) detecting when a predetermined operating parameter of said vibration body reaches a specific value thereof which corresponds to a value of said drive frequency that is higher than said highest resonance frequency and lower than said antiresonance frequency (c) when said specific value is detected, halting said frequency sweeping to thereby fix the value of said drive frequency; (d) monitoring said operating parameter to detect whether the value thereof subsequently deviates from said predetermined value by more than a predetermined permissible range of variation and; (e) if deviation of said operating parameter value outside said permissible range of variation is detected, successively repeating said steps (a) through (d).

Claim 2

A method of driving an ultrasonic motor comprising a vibration body formed of a piezoelectric body and an elastic body and a rotary body which is disposed in contact with said vibration body, the vibration body being driven to vibrate by an alternating drive voltage which is applied to said piezoelectric body for thereby rotating the rotary body by a frictional force, the method comprising successive steps of: (a) sweeping a drive frequency of said vibration body downward from a high end of a predetermined frequency sweep range, said sweep range including at least a frequency range extending between an antiresonance frequency of said vibration body and a highest resonance frequency of said vibration body with respect to a hysteresis loop exhibited by a resonance frequency characteristic of said vibration body; (b) detecting when a predetermined operating parameter of said vibration body reaches a specific value thereof which corresponds to a value of said drive frequency that is higher than said highest resonance frequency and lower than said antiresonance frequency (c) when said specific value is detected, halting said frequency sweeping to thereby fix the value of said drive frequency; (d) monitoring said operating parameter to detect whether the value thereof subsequently deviates from said predetermined value by more than a predetermined permissible range of variation and; (e) if deviation of said operating parameter value outside said permissible range of variation is detected, successively repeating said steps (a) through (d).

Claim 3

A method of driving an ultrasonic motor comprising a vibration body formed of a piezoelectric body and an elastic body and a rotary body which is disposed in contact with said vibration body, the vibration body being driven to vibrate by an alternating drive voltage which is applied to said piezoelectric body for thereby rotating the rotary body by a frictional force, the method comprising successive steps of; (a) sweeping a drive frequency of said vibration body upward from a high end of a predetermined frequency sweep range, said sweep range including at least a frequency range extending between an antiresonance frequency of said vibration body and a highest resonance frequency of said vibration body with respect to a hysteresis loop exhibited by a resonance frequency characteristic of said vibration body; (b) detecting when a predetermined operating parameter of said vibration body reaches a specific value thereof which corresponds to said resonance frequency; (c) when said specific value is detected, halting said frequency sweeping and fixing of said drive frequency at a value which is equal to the drive frequency value at the point of halting said frequency sweeping, incremented by a predetermined amount, said amount being determined such as to set said drive frequency to a value which is higher than said highest resonance frequency and lower than said antiresonance frequency; (d) monitoring said operating parameter to detect whether the value thereof subsequently deviates from said predetermined value by more than a predetermined permissible range of variation and; (e) if deviation of said operating parameter value outside said permissible range of variation is detected, successively repeating said steps (a) through (d).

Claim 4

A method of driving an ultrasonic motor comprising a vibration body formed of a piezoelectric body and an elastic body and a rotary body which is disposed in contact with said vibration body, the vibration body being driven to vibrate by an alternating drive voltage which is applied to said piezoelectric body for thereby rotating the rotary body by a frictional force, the method comprising successive steps of; (a) sweeping a drive frequency of said vibration body upward from a high end of a predetermined frequency sweep range, said sweep range including at least a frequency range extending between an antiresonance frequency of said vibration body and a highest resonance frequency of said vibration body with respect to a hysteresis loop exhibited by a resonance frequency characteristic of said vibration body; (b) detecting when a predetermined operating parameter of said vibration body reaches a specific value thereof which corresponds to said resonance frequency; (c) when said specific value is detected, halting said frequency sweeping and fixing of said drive frequency at a value which is equal to the drive frequency value at the point of halting said frequency sweeping, incremented by a predetermined amount, said amount being determined such as to set said drive frequency to a value which is higher than said highest resonance frequency and lower than said antiresonance frequency; (d) monitoring said operating parameter to detect whether the value thereof subsequently deviates from said predetermined value by more than a predetermined permissible range of variation and; (e) if deviation of said operating parameter value outside said permissible range of variation is detected, successively repeating said steps (a) through (d).

Claim 6

A method of driving an ultrasonic motor having a vibration body formed of an elastic body and a piezoelectric body adapted to be driven by an electric field alternating in polarity, and a rotary body disposed in contact with said vibration body to be driven by elastic traveling waves generated in the vibration body, the method comprising the steps of: (a) executing frequency sweeping of a drive frequency of said alternating electric field; (b) detecting a condition in which a predetermined operating parameter of said ultrasonic motor attains a value corresponding to a value of said drive frequency which is within a specific range that is higher than a frequency range of a hysteresis loop exhibited by said vibration body and is lower than an antiresonant frequency of said vibration body and halting said frequency sweeping when said condition is attained; (c) controlling said drive frequency in accordance with said operating parameter to maintain said drive frequency within said specific range; and, (d) detecting a condition in which said operating parameter deviates from a range of values thereof corresponding to said specific range, and acting in response to said detection to again execute said steps (a) and (b) of frequency sweeping and drive frequency setting.

Claim 7

A method of driving an ultrasonic motor having a vibration body formed of an elastic body and a piezoelectric body adapted to be driven by an electric field alternating in polarity, and a rotary body disposed in contact with said vibration body to be driven by elastic traveling waves generated in the vibration body, the method comprising the steps of: (a) executing frequency sweeping of a drive frequency of said alternating electric field; (b) detecting a condition in which a predetermined operating parameter of said ultrasonic motor attains a value corresponding to a value of said drive frequency which is within a specific range that is higher than a frequency range of a hysteresis loop exhibited by said vibration body and is lower than an antiresonant frequency of said vibration body and halting said frequency sweeping when said condition is attained; (c) controlling said drive frequency in accordance with said operating parameter to maintain said drive frequency within said specific range; and, (d) detecting a condition in which said operating parameter deviates from a range of values thereof corresponding to said specific range, and acting in response to said detection to again execute said steps (a) and (b) of frequency sweeping and drive frequency setting.