Yaskawa MP2200 Machine Controller - Manual (Page 386)

7 Absolute Position Detection
7.1.1 Outline of the Function
7-2
7.1 Absolute Position Detection Function
This section explains the Absolute Position Detection Function in the MP2200/MP2300.
7.1.1 Outline of the Function
The Absolute Position Detection Function detects the position of the machine even if power is turned
OFF. This allows it to establish the machine coordinate system automatically and to begin operating
automatically without having to execute the zero point return (ZRET) command after power is turned
ON.
The following are features of the absolute position detection system.
• Eliminates the need to execute the zero point return after power is turned ON.
• Eliminates the need for a zero point dog and overtravel limit switch.
7.1.2 Basic Terminology
The following explanation for basic terminology used in this chapter is provided to ensure basic
understanding.
( 1 ) Absolute Encoder
Absolute position detection is generally performed in a semi-closed loop using an absolute encoder
built into a Servomotor. The encoder is comprised of a detector that is used to detect absolute
position within one rotation and a counter that is used to count the number of rotations.
( 2 ) Absolute Data
Absolute data that is stored in an absolute encoder is comprised of the number of rotations (N) from
the absolute reference position and position (PO) in a one Servomotor rotation. This absolute data is
read as serial data when the power is turned ON.
All other operations are the same as that for ordinary incremental encoders.
In other words, we can determine the absolute value P from the following equation.
• Absolute value (P) = N × RP + PO
• Number of rotations from the absolute reference position: N
• Number of pulses per one Servomotor rotation: RP
• Position in one Servomotor rotation: PO
( 3 ) Holding Absolute Data
An absolute encoder uses a battery connected to the battery terminals of the SERVOPACK to
maintain absolute data at all times even though power is turned OFF. It also updates data if there is a
change.
( 4 ) Reading Absolute Data
When power is turned ON, absolute data is read to the SERVOPACK as well as to the MP2200/
MP2300, where it is used to automatically calculate the absolute position and set the machine
coordinate system. This way the absolute machine position can be detected and automatic operation
can begin immediately after power is turned ON.