Servo drives provide electrical outputs to servo motors in closed-loop motion control systems that use positional feedback and corrective signals to optimize position, speed, and accuracy. They control one or more axes, provide analog or digital control signals, and often feature integral motion controllers. Servo drives are used with many different types of motors. AC and DC motors feature brushed or brushless designs and are suitable for a variety of industrial applications. Brushed motors provide commutation via physical contacts, usually spring-loaded graphite brushes. Brushless motors provide commutation electronically, without physical brush contact, and use trapezoidal or sinusoidal drives. Trapezoidal servo drives successively energize two motor windings at one time before proceeding to the next pair. Sinusoidal servo drives provide three sinusoidal signals to three motor windings at one time. Other motor types for servo drives include linear motors, voice coil motors, and vector motors.

Differences

Servo drives differ in terms of electrical ratings, operating parameters, configurations, and features. Electrical ratings include maximum output voltage, rated power, continuous output current, peak output current, AC supply voltage, and DC supply voltage. Servo drives use either single-phase or three-phase inputs at 50, 60, or 400 Hz. Operating parameters include specifications for setup and control. Some servo drives have manual controls such as knobs, DIP switches, jumpers or potentiometers. Others include a joystick, digital control panel, computer interface, or slots for PCMCIA cards. Control programs can be stored on removeable, nonvolatile storage media. Hand held devices are designed to be programmed remotely. Wireless and web-enabled controls are also available. Configurations for servo drives include several mounting styles. Most devices mount on a chassis, DIN rail, panel, rack, wall, or printed circuit board (PCB). Standalone devices and integrated circuit (IC) chips that mount on PCBs are also available. Features for servo drives include soft starting; dynamic, injection, or regenerative braking; brake outputs or auxiliary inputs/outputs (I/O); auto-tuning, self-diagnostics, and status monitoring; and alarms for conditions such as overvoltage. 

Buses and Communication Standards

Computer-based servo drives use many different types of buses and communication standards. Bus types include advanced technology attachment (ATA), peripheral component interconnect (PCI), integrated drive electronics (IDE), industry standard architecture (ISA), general-purpose interface bus (GPIB), universal serial bus (USB), and VersaModule Eurocard bus (VMEbus). Communications standards include ARCNET, AS-i, Beckhoff I/O, open computer area network (CANopen) device network (DeviceNet), Ethernet, small computer systems interface (SCSI), smart distributed system (SDS), serial real-time communications system (SERCOS), and transistor-transistor logic (TTL). Serial interfaces such as RS232, RS422, and RS485 are also available.