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3 Key Reasons For Not Taking Shortcuts for Motor Repairs

02 Feb 2015
Paul Coughlin

Brushless AC servo motors and stepper motors have long life spans, which are largely due to the lack of wearing components. Unlike brush type motors, other than the bearings, brushless AC servo motors and stepper motors have no wearing components. Additionally you do not have conductive brush dust, which, as it collects on the commutator, may short the armature.

The radial and axial loading requirements of step and servo motors are based upon the shafts of the motor, which are usually far less than what the bearings are designed to handle, which provides for a healthy motor life span.

However, occasionally motors do need to be repaired. Either a feedback device goes bad, or some kind of electrical mishap may cause the drive to provide too much current, which may damage the winding, or it could be as simple as the bearing grease drying up.

At these times the end user is usually scrambling to get a repair and may consider turning to a local motor repair or re-wind shop.

Old Electric ShopSTOP! Inexperienced shops may cause considerable delays in getting the motor back in proper running condition. Here are three key issues that you should take into account when determining where to get your motor serviced:

  1. In the case of windings, the repair shop may not be able to conduct proper surge tests. This could lead to early failure of the motor and create additional downtime.
  2. In the case of feedbacks, even a simple resolver can give complications for alignment in these shops. Many hours are lost over the phone guiding the repair shop, without the necessary equipment, through proper alignment procedure.
  3. One of the biggest issues repair shops face surround stepper motors and the replacement of bearings. The problem lies in the way the motors are magnetized. For the Brushless AC Servo motor, the rotor is magnetized radially, as a single component, and is then placed into the stator assembly. The Stepper motor is magnetized axially as a complete motor. When you remove the stepper rotor/shaft assembly from the stator you collapse the magnetic field. This causes a loss in torque of up to 50% when reassembled. Most of the repair shops will disassemble the motor, replace the bearings, and re-assemble the motor unaware that the magnetic circuitry has been weakened. The end customer will then receive the repaired motor only to find out that the torque has been severely reduced.

In most cases the time lost in trying to rush brushless AC servo motors and stepper motors through local, unauthorized repair shops increase the downtime to the machine. The end user is frustrated to learn that the motor was not repaired properly or in the case of the stepper motor, needs to be re-magnetized. Consider these three issues if you are ever faced with a motor in need of repair.

About the Author

Paul Coughlin

Paul Coughlin - Author

Paul started his career at Sigma Instruments, Inc., one of the original stepper motor manufactures. Through his career Paul has worked for Pacific Scientific Motors & Controls and the various companies acquired by Danaher such as Superior Electric, American Precision Industries (API), InMotion and Kollmorgen. Paul has held numerous positions throughout his career such as Application Engineer, Stepper Product Specialist, International Sales Engineer, Level 2 Systems Application Engineer and is currently the CS Systems Engineer Team Lead.

Paul has worked many motion technologies, but still enjoys working with and talking about stepper motors. If you want to step through something with Paul, contact him here: Paul Coughlin

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