39
Servo System Precautions
Section 2-4
Connecting master external encoder signal
2-4
Servo System Precautions
The following precautions are directly related to the operation of the servo
system. Refer to 1-4-1 Servo System Principles for a description of servo sys-
tem operation.
The direct connection of the MC Unit to the Servo Driver provides a safe inter-
face without the risk of disconnected or faulty wiring. The interface provides
the MC Unit good monitoring operation to check the state of the Servo Driver
at any given time. The Servo Driver Alarms and Warnings can be quickly dis-
tinguished and appropriate action can be taken.
If the communications between the MC Unit and Servo Driver fail, this is
detected by either of the Units. The system will be halted into a fail-safe state.
For any details about the MC Unit and Servo Driver error handling and alarm
definitions, refer to SECTION 8 Troubleshooting.
Precautions for safe
operation
In a servo system employing a Servomotor, an unforeseen event may cause
the Servomotor to run out of control. Therefore, careful attention must be paid
to include sufficient safety measures into the system design.
To guarantee fail-safe operation for any circumstances or occurrences, the
following precautions must be taken.
Following Error Limit Setting
An important motion control safety precaution of the MC Unit is the following
error limit checking. When the Servomotor is controlled to follow a specific
demanded motion profile, this will always produce a following error between
the demanded and actual measured position.
The maximum allowable value for this following error can be set with the
FE_LIMIT axis parameter. When the following error at one moment exceeds
the limit, a Motion Error will occur. The Servo Driver will be disabled and all
motion will come to a halt. The user must be sure that this does not have an
adverse effect on the machine. Determine the value of following error limit
carefully according to the operating conditions of the application. See 6-3-74
FE_LIMIT for details.
External Limit Switches
The second safety precaution which is required is the use of limit switches.
Monitoring sensors are installed at the edges of the workpiece’s range of
movement to detect abnormal workpiece movement and stop operation if a
runaway occurs.
Although the limit switches can be connected either to the MC Unit as to the
Servo Driver, it is strongly recommended to connect the limit switches to the
MCW151 (input)
1
A+
2
A-
3
B+
4
B-
5
Z+
6
Z-
7
0V_ENC
8
5V_ENC
Encoder
Line Driver output
Example: E6B2-CWZ1X
Black: Phase A+
Black/red: Phase A-
White: Phase B+
White/red: Phase B-
Orange: Phase Z+
Orange/red: Phase Z-
Blue: 0V (COM)
Brown: 5V DC