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The Benefits and Limitations of Drive System Technologies

The Benefits and Limitations of Drive System Technologies

All-electric machines have been working their way into many industries since the 1990s, slowly replacing traditional machines with systems that were hydraulically driven. The original appeal of electric systems is their improvements in efficiency, operational consistency, reliability, and to shed the dirty and often toxic oil leaks often associated with hydraulic systems.

Although they were appealing, engineers quickly realized that contact driven all-electric machines may not be as effective for higher torque applications.  Over time, new drive system technologies have been built that have the capability of driving large/high torque motors, and machine designers are now turning to them as a cost-efficient, power saving, and reliable solutions.

Manufacturers and machine designers have a few options when it comes to basic drive types:

  1. Variable Frequency Drives (VFD) that utilize V/f technology
  2. VFD Drives that utilize Vector Drive Technology
  3. Electric Servo Drives

Each type come with its own advantages and limitations.

Advantages of VFDs with V/f Technology

VFDs generate outputs that drive conventional AC induction motors. In VFDs that use V/f technology, the output can be varied in its frequency. This varies the RPM of the motor. The output voltage is also varied in proportion to the frequency of the motor. VFDs are commonly used in extrusion machines.

The advantages of VFDs that use V/f technology include:

  • Low relative cost
  • Good choice for powering plastic extrusion drives
  • Speed accuracy is consistent with a steady load
  • Speed measuring tachometer can be added to improved speed accuracy over varying loads
  • Good at maintaining the motor’s torque over its usable operating range

Some of their limitations include:

  • Can only provide motor speed accuracies of around ten percent with varying loads
  • Low response to and control over pressure and velocity changes
  • Only usable to about 400-500 RPM.

Advantages of VFDs with Vector Drive Technology

VFDs equipped with Vector Drive Technology utilize microcontrollers to manipulate drive output, allowing users to control the torque of standard AC induction motors, even allowing a reduction to zero RPM.

The advantages of VFDs that use Vector Drive Technology include:

  • The ability to have servo-like control over motors
  • Small additional cost to a VFD
  • Adding electric sensors to the motor allow vector drives to operate at zero RPM and with a high degree of accuracy

Some of their limitations include:

  • Auxiliary air or water cooling is necessary for motors that run at low speeds with high torque to prevent overheating
  • Generally limited to a maximum speed of 2.5-3 times the motor’s rated RPM
  • Driven induction motors must be rated for inverter duty to prevent damage to the bearings

Electric Servo Drives

Electric servo motors are permanent magnet AC motors. They have a high peak torque that far exceeds steady state torque. This gives them the ability to make highly dynamic speed changes. They are standard in most all-electric molding machines.

The advantages of electric servo motors include:

  • Gives users precise control of speed, torque, and the position of the servo motor
  • High speed range
  • Maximum torque available at zero RPM

Some of their limitations include:

  • Require more complex drive electronics
  • Limited horsepower means multiple motors must be installed when power requirements are high
  • Requires additional air or water cooling when operating at zero RPM with high torque

Why Use Drive Technology?

Many drive technologies cut power usage, which can often offset their initial costs. Their high performance operation have made them dominant for many applications ranging from plastic injection machinery to steel coil straightening machinery.  They are a viable enhancement to all-electric motor driven machines. Learn more about the drive systems and products by getting in touch with AMMC today.