Method for detecting original position of robot arm for alignment

Method for detecting an original position of a robot arm which is pivotally mounted at one end thereof comprising the steps of:

• detecting a first angle between an original position of said robot arm and an original position of an absolute position detecting means for detecting the absolute position of the robot arm,
• detecting a second angle between said original position of said robot arm and a position in which a Z-signal which is generated at a predetermined revolution angle of a rotary encoder of incremental type for detecting incremental position of the robot arm is output,
• moving said robot arm to a position wherein a Z-signal is output,
• detecting an absolute position of said robot arm by said absolute position detecting means,
• calculating a difference between said detected value of said absolute position detecting means and a sum of said first angle and said second angle,
• calculating an angle representing the position of said robot arm corresponding to the angle of said difference on the basis of a predetermined relation, and
• caluclating an absolute position of said robot arm by summing said angle respresenting the position of said arm and said second angle.