Positioning device that performs retracting action using air balance

A positioning device comprising:

• a servo motor that drives a vertical axis;
• a controller that controls the servo motor;
• an air balance that cancels a self-weight of the vertical axis, the positioning device further comprising:
• an air supply source that supplies air to the air balance;
• a pressure regulating device that regulates pressure of the air balance using air supplied from the air supply source;
• and
• an air balance pressure modifying unit that modifies the pressure of the air balance and moves the vertical axis in a direction which enables avoiding a collision between a structure that moves with the vertical axis and another structure or reducing a collision therebetween, when an excitation of the servo motor is released due to an emergency stop, a power outage, or another operation performed on the positioning device;
• wherein the air balance pressure modifying unit generates a force that is equal to or greater than a thrust of the servo motor due to a pressure variation of the air balance.