AC Servo Systems, Motors, Drives And Gearboxes

Servo motor systems provide the highest possible level of performance for precise control of position, velocity, and torque.

A standard AC servo system closes the loop on current, velocity, and position (depending on control mode selection).

Most servos systems will also have available controls for proportional gain, integral gain, feed forward compensation, command low pass filter, and notch filter for resonance suppression.

Before we jump into the details, for anyone interested in learning more about servos, motors, gearboxes and industrial controls, we’d recommend the following from Amazon:
A Comprehensible Guide to Servo Motor Sizing ($19.98 – paperback)
Motors for Makers: A Guide to Steppers, Servos, and Other Electrical Machines ($22.18 – paperback )
Servo Motors and Industrial Control Theory ($89.88 – paperback)

Compared to lower-cost stepping systems, an AC servo system provides three key advantages:

• More torque at higher speeds (up to 5,000 rpm)
• Broader range of power (up to 3kW)
• Higher response with closed-loop control (high hit rate without stalling or lost position)

With hundreds of manufacturers, and thousands of options to choose from, let’s select one for an example. (FYI – a great place to start the selection process and get the latest information is from your local electronics parts distributor like Mouser Electronics) The  “SureServo” family of brushless servo systems from Automation Direct is fully digital and offers a rich set of features to cover a broad range of applications. Within this family, engineers can select from eight standard permanent magnet servo motors; In turn, each of these can be operated in combination with one of three standard servo drives. The benefits of this type of combination are:

• Precise control of position, velocity and torque
• Eight standard systems from 100W to 3kW
• Use with DirectLOGIC PLCs or any other host controller
• Drives feature on-board indexer and adaptive tuning modes

For production, in addition to the benefits the designers also need to consider system cost for each type of implementation. A budgetary price for a complete servo system like the one about can start at about $1,000.

Designers also need to look beyond the hardware of the motors and gear-boxes to consider how the system will be controlled, what type of software is available for setting up the servo system and any associated costs (some manufacturers provided free set up setup software, for example SureServo Downloads, while others may have a one time-cost or a per-device licensing fee.

Continuing our example with the SureServo family. These have a robust software control, but the user interface  is designed for flexibility and quick implementation. The drives accept a wide range of command sources:

• Built-in motion controller w/preset position, velocity or torque
• Select presets with switch inputs and/or the multi-drop Modbus serial interface
• Position commands with “pulse and direction” or “count up and down” format
• Analog voltage Velocity or Torque command
• Encoder follower

The user interface is highly intuitive and simple to operate. For configuration, tuning and diagnostics:

• use the drive’s integrated keypad /display
• or take advantage of the free SureServo Pro PC-based software.
• tune the system easily with adaptive auto-tuning selections or a manual mode.

The servo system can also be adapted to diverse applications with configurable I/O, including :

• eight digital inputs,
• five digital outputs,
• two analog monitors
• and a scalable encoder output

Following directly along from the motor selection, is the drive selection. It’s usually simplest to use the same manufacturer for both the motor and the drive. In our example, Automation Direct also features high performance planetary gearboxes. For systems which require precise inertia balancing and quiet operation, the SureGear PGA series have superior specifications. Not to limit their market, these drives also easily mate to SureServo motors, or other manufacturers motors.. Everything needed to mount the SureServo motor is included in the system. Highlights for the SureGear precision gearbox are:

• Four gear ratios available (5, 10, 15, 25:1)
• Mounting hardware included for attaching to SureServo motors
• Industry-standard mounting dimensions
• Thread-in mounting style
• Best-in-class backlash (5 arc-min)

Related Article – Precision Planetary Gearboxes For Servomotors

As with the motor, for other than research and one-off projects, the cost is a key factor for the designer to select at drive. For a budgetary plan, the Servo Amplifiers Drives start at $488.00 (e.g., SVA-2040).

This brings the cost for a motor and drive to around $1.5K for this type of system. For additional information, product details, see the systems overview below:

Complete SureServo AC Servo Systems Overview 

If you want to learn more about servos, motors, gearboxes and industrial controls, we’d recommend the following from Amazon:
A Comprehensible Guide to Servo Motor Sizing ($19.98 – paperback)
Motors for Makers: A Guide to Steppers, Servos, and Other Electrical Machines ($22.18 – paperback )
Servo Motors and Industrial Control Theory ($89.88 – paperback)

It’s worth noting that motors and servo systems come in all types of configurations, specifications and price points. For example, you (or your kids) can get started with New Lego Power Functions Servo Motor ($36.88) mated with LEGO Technic differential gears ($8.49).

***

(Image Credit – Automation Direct)

If you found this article interesting and informative, please be sure to sign up for our weekly e-newsletter as well as daily email / RSS Feeds at SourceTech411  .