Yaskawa Large Capacity Sigma II Series - Manual (Page 21)

1.2 Configuration of Servo System
1-7
1
2. Servomotor
• 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 micropro-
cessor 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 subject to
mechanical wear or aging. For preventive maintenance, inspect and replace parts at reg-
ular intervals. For details, refer to Chapter 8 Inspection, Maintenance, and Trouble-
shooting.
• 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 fre-
quency 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:
Yaskawa SGMBH servomotors are of the synchronous type.
• Performance of Servomotor
A servomotor must have “instantaneous power” so that it can start as soon as a start ref-
erence is received. The term “power rating (kW/s)” is used to represent instantaneous
power. It refers to the electric power (kW) that a servomotor generates per second. The
greater the power rating, the more powerful the 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)