Yaskawa MP920 User's Manual Design - Manual (Page 447)

10 Absolute Position Detection
10.1.1 Description of the Function
10-2
10.1 Structure of the Absolute Position Detection Function
This section describes the Absolute Position Detection Function in the MP920.
10.1.1 Description of the Function
The Absolute Position Detection Function detects the position of the machine even if power
is turned OFF. This allows it to set the machine coordinate system automatically and to
begin operating automatically without having to return to the zero point after power is turned
ON.
The following are features of the absolute position detection system.
• Eliminates the need to return to the zero point after power is turned ON.
• Eliminates the need for a zero point dog and overtravel limit switch.
10.1.2 Structure of Absolute Position Detection
„ Basic Terminology
The following explanation for basic terminology used in this chapter is provided to ensure
basic understanding.
Absolute Encoder
Absolute position detection is generally performed in a semi-closed loop using an absolute
encoder built into a Servomotor. The detector is comprised of an encoder that is used to
detect absolute position within one rotation and a counter that is used to count the number of
rotations.
Absolute Data
Absolute data that is stored in an absolute encoder is comprised of the number of rotations
(P) from the absolute reference position and position (PO) in a one Servomotor rotation.
This absolute data is read as serial data when the machine is turned ON.
All other operations are the same as that for ordinary incremental encoders.
In other words, we can determine the absolute position PO from the equation for absolute
value (P) which is absolute value (P) = N
× PR+ PO if we use the following:
• Number of rotations from the absolute reference position: N
• Number of pulses per one Servomotor rotation: PR
• Position in one Servomotor rotation: PO