Abstract: A surveying instrument assumes either a high-speed drive control mode for driving a surveying optical system at high speed or a low-speed drive control mode for driving the surveying optical system at low speed. A motor is continuously driven through a PWM control method in the high-speed drive control mode. Then, the low-speed drive control mode is selected to drive the motor so as to allow the motor to alternate acceleration and a virtual stop. As the surveying optical system approaches a predetermined position, a condition for next motor acceleration is set based upon the detected rotational angle of the surveying optical system. Thus, it becomes possible to stop the surveying optical system at the predetermined position with a high degree of accuracy.

Abstract: By providing a diffusing plate between a laser diode and an objective lens, a measurement light flux emitted from the laser diode is irradiated on a corner cube in a defocused state via the objective lens. The light flux having been reflected at corner cube sustains the defocused state. The reflected light flux having been reflected at and having exited the corner cube becomes condensed onto an avalanche photodiode through the objective lens. Even when a vibration occurs at the corner cube, the reflected light flux is received at the avalanche photodiode as long as the light flux having been reflected at and having exited the corner cube is within the predetermined range.

Abstract: A surveying instrument assumes either a high-speed drive control mode for driving a surveying optical system at high speed or a low-speed drive control mode for driving the surveying optical system at low speed. A motor is continuously driven through a PWM control method in the high-speed drive control mode. Then, the low-speed drive control mode is selected to drive the motor so as to allow the motor to alternate acceleration and a virtual stop. As the surveying optical system approaches a predetermined position, a condition for next motor acceleration is set based upon the detected rotational angle of the surveying optical system. Thus, it becomes possible to stop the surveying optical system at the predetermined position with a high degree of accuracy.