SSt-1500-VCx
DSP-Based Digital Servo Drive
The SSt-1500-V is the latest in Teknic’s line of DSP-based servo drives. This unit improves on its predecessor’s ability as a high-bandwidth, fully digital, DSP-based amplifier that accepts ±10V analog torque or velocity commands. Upgrading a conventional “dumb” amplifier to an SSt-1500-V will improve tracking, smoothness and settling time.
In velocity mode, the drive utilizes a proprietary servo algorithm that delivers microsecond level response to velocity errors to permit precise motor control. Moreover, this algorithm helps the drive to distinguish between motor feedback quantization errors and real velocity errors to eliminate self-generating velocity error.
In addition to a unique servo algorithm, the drive removes a little-known flaw present in other amplifiers to further optimize motor performance. All other amplifiers servo control current, not torque. So, servo systems that use other amplifiers actually run open-loop with respect to torque!
Servo controlling torque requires synchronized control of all motor phases with respect to the magnetic field of the motor’s rotor. Conventional amps control each motor phase with a separate, dissociated current loop servo. This scheme ignores the fact that the motor phases are tied together and thus interdependent. Furthermore, small errors in each phase can combine to create a large vector (torque) error. These torque errors lead to inadvertent velocity errors.
The SSt-1500-V employs a proprietary torque control method: sinewave, vector feed-forward with DQ decoupling. This method constantly measures all the variables required to accurately calculate the true torque output (and the out-of-phase currents which only heat the motor) and continuously works to servo the torque to the commanded value and the out-of-phase currents to zero. So in the SSt, the torque is truly under closed-loop control. This actively removes errors in motor torque and preempts the resulting velocity error.
So, with the same servo controller, OEMs will see smoother motion and tighter velocity control by simply replacing their velocity amplifiers with SSt-1500-V drives.