Failsafe Principles; Failures In The Command System - Omron CS1W-MC221 - 02-2008 Operation Manual

Failsafe Circuits
2-4-1

Failsafe Principles

Item
Outline Movements are not performed at the command
speed or in the desired direction.
Location of failure Digital-to-analog circuits or analog power circuits
in the MC Unit.
Analog-to-digital circuits in Servo Drive, wiring of
command systems, etc.
Failsafe measures Installing sensors in dangerous locations to stop the mechanical system by turning OFF the Servo
Drive main circuits.
Remarks Machine movements can be determined from the
amount of movement in the encoder, which in
turn can be determined by the value of the error
counter. The following measures can thus be
taken.
Creating a system that will stop the motor for the
error counter warning function.
Creating a system that will stop the motor for the
error counter overflow function.
If the command from the MC Unit is within a
range determined to be, zones can be set and
used to sop the motor.
2-4-2

Failures in the Command System

Stopping the Motor with an Error Counter Warning
Error Counter Warnings
1,2,3...
134
The MC Unit handles failsafe measures as described in the following table.
Applications examples are provided in the following sections.
Failure in the command system
The Error Counter Warning Flag will be turned ON to notify the CPU Unit if the
number of pulses in the error counter exceeds the value set as the Error
Counter Warning Value in the System Parameters. The Error Counter Warn-
ing Flag can be monitored in the ladder program to handle errors if they occur.
Use the following procedure to set the Error Counter Warning Value.
1. Move the system in trial operation and check the number of pulses that ac-
cumulate in the error counter.
2. After confirming the maximum number of pulses in the error counter, set
the Error Counter Warning Value in the System Parameters to between
10% and 20% higher than the maximum number.
Refer to Error Counter Function Selection Bit in 5-4-1 System Controls for
more information.
Failure in the feedback system
Movement occurs for stop commands or
movement is not performed in the desired
direction.
Motor encoder, encoder cable, Servo Drive
encoder circuit, MC Unit encoder circuit.
If the feedback system fails, it will not be possible
to determine the position of the mechanical
system, e.g., the amount of encoder movement
will be 0 even though the machine is moving.
Here, hardware measures, such as sensors to
stop movement, are required.
Section 2-4