Patent ID: 7489765

Claim:
A collimator control method for controlling a collimator that includes motor-driven blades, comprising the steps of: using an encoder to encode rotations made by a motor; using a decoder to decode a signal sent from the encoder; using a sensor to sense whether the blades exist at zero positions; positioning, when the collimator enters a homing phase in a first control state, the blades on the basis of a blade sense signal sent from the sensor, and if the sensor has not sensed the blades but the rotational velocity of the motor has decreased to fall below a predetermined velocity, switching the first control state to the second control state; switching the first control state to the second control state when the collimator enters a working phase in the first control state and when an overshoot made by the blades returning to the zero positions exceeds a predetermined limit; forcibly reversing, when the second control state is designated, the rotating direction of the motor so as to withdraw the blades, and if an operator performs a manipulation to reset the collimator to the first control state, resetting the collimator to the first control state based on tentative zero positions or the first control state based on the sense signal sent from the sensor according to whether the sensor has failed.