Servo Drive FAQ

What are Analog Servo Drives?

Our analog drive family contains drives that can power Single Phase (Brushed) and Three Phase (Brushless) motors. Analog drives are powered off either a single DC or AC (1Ø or 3Ø) power supply, and provide a variety of control and feedback options. The drives accept either a ±10V analog signal, a PWM and Direction signal, or two sinusoidal command signals as input. The signal can represent either a motor torque or velocity command. A digital controller can be used to command and interact with analog servo drives, and a number of input/output pins are available for parameter observation and drive configuration. Analog servo drives are used extensively in motion control systems where precise control of position and/or velocity is required. The analog drive converts the low-energy reference signals from the controller into high-energy signals (motor voltage and current.)

What are the differences between Sinusoidal vs. Trapezoidal Servo Drives?

DC brushless amplifiers (a.k.a. trapezoidal, 6-step or 12-step) use Hall Effect sensor signals for commutation feedback. The Hall Effect sensors (typically three) are built into the motor to detect the position of the rotor magnetic field. These sensors are mounted such that they each generate a square wave with 120-degree phase difference, over one electrical cycle of the motor. The amplifier drives two of the three motor phases with DC current during each specific Hall sensor state. This commutation technique results in a very cost-effective amplifier although the torque ripple with trapezoidal drives is very high, measuring about 13.4% when used with motors with sinusoidal back-EMF.

AC brushless amplifiers (a.k.a. sinusoidal, sine wave) use encoder or resolver signals for commutation feedback. The amplifier drives the motor with sinusoidal currents, resulting in smooth motion (no torque ripple). This amplifier is more complex since it needs to accept high-resolution position feedback. Such amplifiers use a micro-controller implementation for the sinusoidal commutation. When encoder feedback information is used for commutation, Hall Effect sensors are still needed for startup since the encoder provides only incremental position information. Resolvers provide absolute position information and therefore no additional sensors are required. 

What are Digital Servo Drives?

Electromate®’s digital drives deliver peak power output from 1.5 to 27.4kW, and support an array of feedback options. Driving single phase, three phase, and closed loop vector motors with the ability to interface with both digital network commands and traditional ±10V analog commands, our digital drives offer a versatile blend of cutting edge technology and proven results.

Digital servo drives feature:

  • Universal servo motor capability by means of automatic commutation adjustment
  • Variety of feedback options – Absolute Encoder (Heidenhain EnDat® or Stegmann Hiperface®), Sin/Cos Encoder, Incremental Encoder, Hall Sensors, Resolver, Tachometer, Potentiometer
  • Full tuning control of Position, Velocity, and Torque Loops
  • Real-time oscilloscope for high performance tuning
  • Status panel for drive and system diagnostics
  • I/O configuration for over 60 events and signals
  • Dual loop feedback and control - increases stability and accuracy
  • Stand-alone or network configuration

What are Single Phase Brushed Servo Drives?

Brushed type servo drives are designed for use with permanent magnet brushed DC motors (PMDC motors). PMDC motors have a single winding (armature) on the rotor, and permanent magnets on the stator (no field winding). Brushes and commutators maintain the optimum torque angle. The torque generated by a PMDC motor is proportional to the current, giving it excellent dynamic control capabilities in motion control systems. Brushed drives can also be used to control current in other inductive loads such as voice coil actuators, magnetic bearings, etc.

What are Three Phased  Brushless Servo Drives?

Three Phase (brushless) servo drives are used with brushless servo motors. These motors typically have a three-phase winding on the stator and permanent magnets on the rotor. Brushless motors require commutation feedback for proper operation (the commutators and brushes perform this function on brush type motors). This feedback consists of rotor magnetic field orientation information, supplied either by magnetic field sensors (Hall Effect sensors) or position sensors (encoder or resolver). Brushless motors have better power density ratings than brushed motors because heat is generated in the stator, resulting in a shorter thermal path to the outside environment.

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