Encoder Alignment: Isn’t Important – It’s Critical
Servo motor issues can be traced to any number of areas such as dirt, grease, cracked housings, excessive vibration, extreme temperatures, and so on. However, the problem is often related to the servo motor encoder. More specifically, problems with the encoder alignment. Even if the servo motor and encoder are functioning perfectly, failure could occur simply due to an incorrect alignment angle.
The encoder alignment angle is the relationship between the encoder and the motor windings. And this association is extremely important. Encoders must be aligned with sufficient accuracy so that the motor can be correctly commutated by the drive, and can provide the torque and velocity that is commanded by the controller for the application. Even slight alignment variations can cause the motor to run poorly or not at all.
In this blog we’ll take a closer look at servo motor encoder alignment causes, effects, and ways to ensure proper alignment.
How to Tell if an Encoder is Properly Aligned
Servo motor alignment should be checked whenever a motor is suspected to be defective. Symptoms of misalignment include overheating, overcurrent, motor vibration, and so on. Because these issues can be traced to many areas, alignment issues are easily misdiagnosed as a winding, magnet, or bearing problem.
While there are many ways that a servo can become misaligned, a leading culprit is human error. Encoders are routinely removed from the servo motor for nearly any type of maintenance or repair. And this opens the door to potential problems as servos sometimes return from repair misaligned. Because of this they should be closely examined and tested prior to returning to service.
How to Align Your Servo Motor Encoder
While manually aligning a servo motor encoder can seem like a complex procedure, it gets easier with experience. The process begins with determining the motor and encoder forward directions as well as the number of magnet poles, which enables the calculation of a very important figure: the electrical angle of the motor. The encoder is then adjusted to a specific electrical angle as required by the servo motor drive.
Mitchell Electronics, Inc. Vice President, Stuart Mitchell offers some suggestions to this step. “The encoder count is useful in telling us the position of the encoder, but that depends completely on the resolution of the encoder, and this varies across the industry. It can be helpful to think in terms of an electrical angle because it allows you to standardize your alignment process regardless of the encoder resolution or number of servo motor poles. An alignment within plus or minus three electrical degrees provides you with a servo motor that will run efficiently in most applications.”
Sometimes the drive manufacturer does not specify a standard alignment for the encoder. In these cases, angles are stored inside the encoder memory. Mitchell adds, “This process actually can save time and reduce errors assuming that you have the capability to measure the current alignment angle and then program it into the encoder memory after reassembly.”
Servo Motor Alignment Tools
There is various equipment available to assist with alignment. Oscilloscopes, servo motor drives, or other manufacturer specific products can be used to confirm signal line voltages or view error codes. However, as Stuart Mitchell explained, they have their limitations. “Much of this equipment is not actually specifically designed for encoder testing and alignment. As a result, manual iterations of the process or further interpretation of results is often required. And because tools or processes may differ from one motor manufacturer to another, some methods still require hand calculations along with trial and error.”
To address this problem, Mitchell Electronics has developed solutions to make alignment more automated, easy, and reliable.
- Mitchell’s Athena software calculates important figures and offers a quick and repeatable process that can be applied to a range of servo motor manufacturers.
- The TI-5000JX encoder tester confirms encoder status such as counting, error codes, and alignment angle. The product can also test and reprogram encoder memory.
- The TI-3000JX is a servo motor run test product which is used to run a permanent magnet brushless AC or DC servo motor. Manufacturer specific servo motor drives can be excellent for verifying servo motors but can be difficult and time consuming to configure. It is also not always practical to have a spare servo motor drive for every servo motor that you wish to run. The TI-3000JX is a run test product which acts as a universal servo motor drive providing a diagnostic test before or after a servo motor repair.
- The TI-5106 is a new hardware adapter which enables support for the 2-wire Sick Hiperface DSL protocol including the ability to perform a Count Test, display electrical angles, set alignment electronically, receive error codes, read, and write memory data from supported manufacturers, and run-test motors.
- From tutorials, blogs, and videos to direct support, Mitchell Electronics, Inc. also offers a variety of training and support services to assist with servo motor repair and encoder alignment. No matter if you’re a novice or seasoned veteran, we have the level of help tailored for your needs and applications.
A growing number of repair shops and manufacturers are servicing servo motors and ensuring proper encoder alignment with Mitchell’s products. Visit us online at www.mitchell-electronics.com. We also have an active YouTube channel with troubleshoot videos and tutorials. Finally, you can always give us a call at 740-594-8532.