Servo Motor Feedback Devices - Summary and Recommendations

Choosing the Right Rotary Servo Feedback Device - Part 3 Servo Motors Electromechanical and Drives Division North America This is the final of a three-part series that spoke to the various feedback devices that are provided as options on Parker Servo Motors. Part 1 & Part 2 provided the basic theory of operation for the devices and provided some guidance on why you might choose one versus the other, along with some helpful formulas for calculating required resolution. The following is a quick summary and recommendations on selecting the best feedback device for your motion control application.

Summary and recommendations

Incremental encoders (optical)

Choosing the Right Rotary Servo Feedback Device Servo Motor Electromechanical and Drives Division

Good resolution - up to 20,000 ppr on standard Parker product
Good for applications where going back to home for out of application situation (power down) is not a concern
Low cost

Absolute encoders

Choosing the Right Rotary Servo Feedback Device Servo Motor Electromechanical Division

Provide absolute position upon powering up (no homing required)
Provide a very high resolution
- 16 bit = 65,536 ppr
- 20 bit = 1,048,576 ppr
Options for memory download to support “smart” encoder option
Option to allow for single cable from the motor for power and feedback

Resolver

Choosing the Right Rotary Servo Feedback Device - Parker Servo Motor - Parker Electromechanical Division

Good resolution (12 bit)
Very rugged – 40g vibration and 200g shock
High temp suitability – up to 200 deg. C
Provide absolute position within a single turn
Accuracy not as good as incremental or absolute encoders
Low cost

Performance needs

Speed and position control
- Understand your resolution requirement
- Select your feedback device based on the environment and the aforementioned pros and cons
Torque Control
- Feedback only provides position data to support the commutation of the motor. Go with resolver or incremental to save money

Learn More

Watch this video to learn more about the features and benefits of the Parker K series frameless servo motor. The feedback devices referred to above can be readily used with this motor.

Jeff Nazzaro - Parker Servo Motor - Parker Electromechanical Division Article contributed by Jeff Nazzaro, gearhead and motor product manager, Electromechanical & Drives Division, Parker Hannifin Corporation.