Yaskawa SGDB - Manual (Page 19)

1.2 Servo Configuration
7
(2) Servomotor
(a) DC servomotor and AC servomotor
Servomotors are divided into two types: DC servomotors and AC servomotors.
DC servomotors are driven by direct current (DC). They have a long history. Up
until the 1980s, the term “servomotor” used to imply a DC servomotor.
From 1984, AC servomotors were emerging as a result of rapid progress in micro-
processor technology. Driven by alternating current (AC), AC servomotors are
now widely used because of the following advantages:
• Easy maintenance: No brush
• High speed: No limitation in rectification rate
Note however that servomotors and SERVOPACKs use some parts that are sub-
ject to mechanical wear or aging. For preventive maintenance, inspect and re-
place parts at regular intervals.
For details, refer to Chapter 6 Inspection, Maintenance, and Troubleshooting.
(b) AC servomotor
AC servomotors are divided into two types: synchronous type and induction type.
The synchronous type is more commonly used.
For a synchronous type servomotor, motor speed is controlled by changing the
frequency of alternating current.
A synchronous type servomotor provides strong holding torque when stopped, so
this type is ideal when precise positioning is required. Use this type for a servo
mechanism for position control.
The following figure illustrates the structure of a synchronous type servomotor:
Light-emitting
element
Rotary disc
Light-receiving
element Armature
wire
Housing
Stator core
Front cap
Ball bearing
Shaft
Rotor core
Magnet
Lead wire
Position detector
(encoder)
Yaskawa SGMj servomotors are of the synchronous type.
1