Absolute Position Detection; Overview Of Absolute Position Detection - YASKAWA E-V-SD Series User Manual

4.5

Absolute Position Detection

An absolute position detection system can be constructed with a host controller when a servomotor with an
absolute encoder is used. An absolute position detection system eliminates the need for homing after the
power supply is turned ON, but the following must be set up to use such a system.
• Initialization of the absolute encoder
• Machine coordinate system settings and sequence execution
• Reading the position of the absolute encoder after the power supply is turned ON and setting the machine
coordinate system
Terminology: Absolute Encoder
There are two types of servomotor encoders. An incremental encoder detects a position by calculating the
difference from home position. An absolute encoder detects the absolute position relative to a reference
position.
The absolute encoder uses a battery connected to the battery terminals of the power regeneration converter
to maintain the absolute value data at all times, even when the power supply is turned OFF. It also updates
the absolute value data if the position changes while the power supply is OFF.
The absolute encoder consists of a detector that is used to detect the absolute position within one rotation
and a counter that is used to count the number of rotations.

4.5.1 Overview of Absolute Position Detection

To read the absolute value data from the absolute encoder to the host controller, turn ON the host controller
and the SERVOPACK at the same time or turn ON the SERVOPACK first.
The following diagram shows an overview of absolute position detection.
Controller
Reference
function
generator
Requesting Sensor Initialization
The host controller sends a request to the SERVOPACK to initialize the sensor when MECHATROLINK-III
communications are established.
Transferring Absolute Value Data (N.PO)
The SERVOPACK obtains the multi-turn data (N) and the initial incremental pulses (PO) when the sensor
initialization request is received.
Creating Position Information
The SERVOPACK creates the position data according to the multiturn data and initial incremental pulses.
Reading Position Information and Absolute Value Data
The host controller reads the position data or absolute value data from the SERVOPACK.
Electronic Gear Conversion
The host controller calculates the absolute value from the read information, performs the electric gear con-
version, and sets the machine coordinate system. The machine coordinate system origin offset must be set in
the SERVOPACK or at the host controller in advance.
For details, refer to 4.5.6 Origin Offset.
This allows an absolute position detection system to detect the absolute position of the machine immediately
after the power supply is turned ON so that machine operation can be started immediately.
Requesting sensor
initialization
Electronic
gear
conversion
MECHATROLINK-III
and
machine
coordinate
system
Reading position
calculations
information and
absolute value data

4.5 Absolute Position Detection

Σ-V-SD-series Driver
Transferring absolute
Creating position
value data (N and PO)
information
Motor
Encoder
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