DC Brushed Servo Motor Refurbishment

What does Refurbishment mean? Is it just another word for repair? NO. At Servotech, brushed DC servo refurbishing meets an extremely high standard of repair, a standard we feel should be expected for all work on servos. For some people, repair and refurbishment are just a label that simply means a servo motor’s bearings were changed, and when all to bolts were put back into it, the motor spun.

Proper Brushed Motor Refurbishing is More than a Bearing Change

Brushed DC servo motors are extremely delicate. Brushes, made of carbon, wear down with every hour of operation. After a few years the build up of carbon can be so immense that even if the motor is in good shape, the carbon residue can be enough to cause a short in the windings, or between commutator bars. A botched rebuild can land a brush rigging out of place. Improperly shimmed and tensioned bearings can force brushes to hit the commutator unevenly. Even just bolting an end bell on in the wrong orientation can result in a motor that does not run in the proper direction.

But completing these actions properly does not mean a servo motor has been properly refurbished. Those are just the basic steps.

Servotech Rebuilt Servo Motor Brake Padbrush dc servo motor repairRepaired Baldor Servo Motor

Our DC Brushed Servo Motor Refurbishing Process

Refurbishment, means re-magnetizing field frames and Tach fields – because over time the vibration and heat from operation degrades magnetism. Repaired motors have degraded magnets – refurbished ones have saturated magnetism.

Refurbishment means turning and undercutting commutators. Brushes will wear ridges into commutators, creating an uneven surface that can even create side wear – a very bad situation because changes in the geometry of the brush and can cause extreme high current. Repaired and refurbished servo motors get new brushes, and are turned in a lathe to create a new even surface for brushes to ride on. Then each commutator bar is cleaned out with a special tool that removes dirt and mica. All armatures are then balanced to make sure the newly refinished surface will wear evenly.

Refurbishment means setting neutral. Repaired motors go back together and they “run”, but refurbished DC brush motors also need to undergo a process called “setting neutral”. An important effort requires an oscilloscope and very accurate power supplies, as neutral determines the smoothness of operation. At Servotech, brushed servo motors are meticulously tuned to ensure proper operation, acceleration and torque. Refurbishment means understanding bearing pre-load. Repaired servo motors have new bearings installed, however new bearings do no account for worn fits or bearing journals, nor do they fix broken or worn bearing shims and wave washers. A brushed servo motor depends on proper bearing pre-load. A motor must run smoothly both cold and when it has reached full operational temperature. Small mechanical inconsistencies will become exacerbated by heat expansion unless the pre-load is set properly.

Refurbishment takes feedback tuning. Some companies will say that if a servo motor encoder produces signals both before and after servo motor rebuild, than the motor is repaired. At Servotech we know an encoder should produce pristine square waves, with proper output voltage levels, phase symmetry, and reliability at high speed. Encoder repairs are often outside the realm of expertise for some repair shops. At Servotech, we are committed to excellence in all aspects of servo motor refurbishment. Any servo encoder that cannot be tuned back to “like new” condition is replaced with a brand new encoder. Lack of a direct replacement does not constitute a lack of ability to replace a feedback device. Our servo refurbishment process includes a strong, new feedback device that will last for thousands of continuous operation hours without a loss of accuracy or reliability.

Refurbishment includes protection. Cutting fluid, coolant, and water can all be present in a servo motor’s operational environment. While a repaired motor may simply be cleaned, a refurbished servo motor is disassembled, washed, baked, rebuilt, sealed, and painted with a two part epoxy coating – the same coating used by the U.S. Navy on submarines. This ensures that a clean environment inside the motor, and that it can remain contaminant free throughout the lifetime of the servo.

DC Brushed Servo Motor balance
Brushed servo motors are tested to the highest quality standards.

The Importance of Proper DC Brushed Servo Motor Refurbishing

Brushed DC servo motors are tough, machines employed in harsh environments. In every hour of operation the servo motor is exposed to vibration, heat, electrical noise and contaminants. Even running by itself on a bench, a DC servo motor creates heat and a certain amount of vibration. All of these variables will degrade a motor’s ability to perform. Magnetism, electrical integrity, mechanical structures, shims, gaskets, greases and fits will all wear down given a long enough amount of time.

Each system that is not refurbished back up to “like new” will only continue to degrade, and do so more quickly. Not undercutting a servo motor commutator means changing the brushes much more often. Not repairing servo encoders means missed counts, lost accuracy or perhaps even a complete failure of the feedback device resulting in a downed machine. At Servotech, refurbishment means breathing life back into a motor – and returning that motor “like new”.

At Servotech, we are committed to the highest quality standards when refurbishing servo motors. Contact us today and request a free quote for your brushless servo motor.

DC Brushed Servo Motor Fanuc
We repair DC Servo Motors large and small!  The motor above is a large Fanuc 10L DC motor utilized in a punch machine.  Below is a lot of small DC servo motors utilized in automated cutting equipment
A magnetic charge fixture sits inside a field frame with degraded magnets.