Patent ID: 7439701
Filing Date: 2008-10-21
Classification: G01D,G01R,H02P

Abstract:
1. A method of detecting an initial excitation phase of a stepping motor, in which at a stop position of a driven member driven by a stepping motor driven with a microstep obtained by dividing one step of a full step drive into m×n, m: integer equal to 1 or more than 1, n: integer equal to 2 or more than 2, a rotation of the driven member in a reverse rotation direction being forcedly stopped by a stopper, an initial excitation phase at which a rotor of the stepping motor is in a stable condition is detected on the basis of whether or not the rotor rotates judged from a pattern of an induced electromotive force generated in an exciting coil in a non-excitation state of the stepping motor during the full step drive, the method comprising: a first step in which the full step drive of the stepping motor causing the rotor to rotate in a reverse rotation direction thereof is performed until a first excitation phase is attained at which the rotor is judged not rotating, a rotation of the rotor in the reverse rotation direction thereof causing the driven member to rotate in the reverse rotation direction thereof; a second step in which the stepping motor is subjected to the microstep drive in the reverse rotation direction of the rotor from a second excitation phase to a third excitation phase, an excitation phase being shifted in the reverse rotation direction of the rotor by an angle, which is obtained by subtracting two step angles of the full step drive of the stepping motor from 180 degrees, so as to reach the second excitation phase from the first excitation phase, and the excitation phase being shifted in the reverse rotation direction of the rotor by m steps of the microstep drive of the stepping motor so as to reach the third excitation phase from the second excitation phase; a third step in which the stepping motor is subjected to the full step drive in a positive or reverse rotation direction of the rotor in a given range of the excitation phase between the third excitation phase and a fourth excitation phase and it is judged whether or not the rotor rotates during the full step drive, the excitation phase being shifted in the positive rotation direction of the rotor by one step of the full step drive of the stepping motor so as to reach the fourth excitation phase from the first excitation phase, a rotation of the rotor in the positive rotation direction thereof causing the driven member to rotate in a positive rotation direction thereof; and a fourth step in which if the rotor is judged rotating in the third step, a fifth excitation phase shifted by 180 degrees from the third excitation phase is determined to be the initial excitation phase and stored in a storage means, wherein if the rotor is judged not rotating, the third excitation phase is shifted by m steps of the microstep drive of the stepping motor in the reverse rotation direction of the rotor and the second step and the third step are repeatedly performed until the rotor is judged rotating in the third step.