Omron C200H-MC221 -, Operation Manual

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7-1 Introduction
This section will describe methods of origin search for motion control systems
using either incremental encoders or absolute encoders.
Using Incremental Encoders
In motion control systems using incremental encoders, the location of the origin
must be fixed after the power is turned ON. There are two ways to fix the origin in
MC Units.
Operation Description
Current position preset The origin is fixed by setting the position where the motor
is stopped to an arbitrary value.
Origin search The origin is fixed by moving the motor and using the limit
switches, origin proximity switches, and encoder’s
Z-phase signals.
If the Machine Parameter’s Origin Search Method
parameter is set to “Set origin at power ON,” the Unit will
automatically fix the position when power is turned ON as
the origin, without moving the motor.
The current position preset operation can be performed by turning ON the Cur-
rent Position Preset Bit (X axis: n+5 bit 05; Y axis: n+7 bit 05) or executing func-
tion G54 (CHANGE REFERENCE COORDINATE SYSTEM PV).
The origin search operation can be performed by turning ON the Origin Search
Bit (X axis: n+5 bit 01; Y axis: n+7 bit 01) or executing function G28 (ORIGIN
SEARCH). An origin search can also be started from the Teaching Box.
Refer to
Sections 7-2 to 7-4 for determining the origin.
Using Absolute Encoders
The absolute encoders retain absolute data by using the backup batteries when
the power to the MC Unit or Servodrivers are turned OFF.
When the power to the MC Unit is turned ON again and if the system is set to the
servo lock state, absolute data will be read from the absolute encoder to deter-
mine the present position. No origin search is required.
Absolute Encoder Setup
When an absolute encoder is installed for the first time, when the battery is
replaced, or when the encoder cable between the Servodriver and motor is
removed for a long time, the absolute data must be defined. This is called “ABS
Initialization.”
When making fine adjustments on the present value after the ABS Initialization,
execute the “ABS Soft Reset.”
For further details, refer to
Sections 7-5 to 7-8 .
The ABS Initialization and ABS Soft Reset can be executed from the interface
area (bits 06 and 07 of n+5 words) or from the Teaching Box. For executing from
the interface area, refer to Section 6 PC Data Area Interface . For executing from
the Teaching Box, refer to the Teaching Box Operation Manual.
7-2 Sensors Required for an Origin Search
The following sensors and conditions are required in order to perform an origin
search.
Sensor Description
CW and CCW limit switches Normally closed inputs are required.
Origin proximity switch The logic of this sensor can be changed in the
Machine Parameters, so either normally closed or
normally open inputs can be used.
Encoder’s Z-phase signal The MC Unit detects the signal when it changes
from Low to High.
Sensors Required for an Origin Search
Section 7-2