After logging in the servo motor and recording the customer information, manufacturer, model number, serial number, purchase order, and tracking or reference numbers, a fax is sent to the customer acknowledging receipt of the motor.
The servo motor is sent to the technician who notes nameplate information, lists power and feedback connector pin-outs, and inspects the servo motor and feedback devices).
If the servo motor has a brake, it is engaged and disengaged to check for proper operation. The amperage is checked and noted. We then note the holding torque (cold) in three positions to make sure it meets or exceeds the manufacturer’s specifications. Later in the run-in process, if the servo motor can be run, the holding torque is again checked after the servo motor has risen to running temperature.
Each of the three windings of the stator is checked with a megger for phase to phase or phase to ground shorts. Resistance levels are checked and noted. Should low resistance levels be found, we will wash and bake the stator to see if the proper resistance levels can be reached. If not, a rewind will be required.
The shaft of the servo motor is coupled to an external drive and the rotor is spun at 1000 RPMs. Because brushless servo motors have a permanent magnet rotor and a wound stator, the servo motor, when back-driven will produce a specific amount of BEMF (back electric motor force). If the BEMF generated is proper we know the magnets are fully charged and the motor will carry the rated load.
We use Mitchell Electronics test equipment to test the feedback devices. This equipment allows us to check each signal coming from the feedback device and all signals simultaneously and test the feedback as a unit.
Should a problem be found with an encoder, normally, a new encoder can be ordered or a replacement found. However, new encoders are expensive and many are obsolete and cannot be bought anymore. Unless we hear from our customer to rush the repair, we will quote the motor repair based on a repaired encoder. Encoder repair can extend the turn around time for a repair by a month or two. It normally takes about two weeks to have the encoder repair quoted (you will receive a quotation from Southeast Servo when we get a quote for the encoder repair). You should expect it to take an additional two weeks after the quote has been approved for Southeast Servo to have the encoder repaired and reassemble, align, and test the servo motor.
Should the servo motor have a resolver, the sine and cosine wave forms are checked for proper voltage levels and phase relationship. If possible, alignment of the resolver is checked and recorded. A graft showing the sine and cosine waves superimposed on the BEMF of the rotor is stored to show how the resolver was aligned with the rotor when it was received.
If the servo motor has hall sensors, we will check alignment, and stored to show they were aligned with the rotor when it was received.
Tachometers are checked for proper voltage levels across their entire speed range.
If possible, the servo motor is then test run using our test drive based on the commutation pulses from the feedback of the motor that is being repaired. RPMs, volts, and amperage are documented for reference.
The servo motor is then disassembled to be visually inspected for worn, damaged, or broken parts. End frames are checked for wear. If a bearing is found to be wobbling or spinning in the end frame, the end frame will be machined and sleeved to ensure a snug fit. All parts are cleaned, some bead blasted, and inspected for damage or wear. If required, the stator will be washed and baked or rewound and the stator windings again tested.
After the above procedures and tests have been completed, the technician determines the parts that he needs. Prices and availability are checked. He reports what he found wrong with the servo motor, what he thinks may have caused the problem, and what he will have to do to repair the servo motor. Costs are gathered for parts, machining, labor, and repairs. We then can quote a repair price and an estimated delivery.
After the repair has been approved by the customer, parts are ordered, machine work begins, and encoder repairs are initiated. Should the windings need rewinding, that process will begin.
After all vendor parts are received, new bearings are installed on all repaired motors. Rotor security and balance are checked. O rings, gaskets, and seals are inspected and replaced if needed. Should contamination be found inside the motor, we will seal the end frames with an extra gasket to prevent contaminates from entering the motor through the gap between the end frame and the stator. Additionally, the power connector and the feedback connector are filled with silacone or other sealing material to prevent contamination. Finally, we epoxy coat the entire motor with epoxy based paint encapsulating the servo motor in a hard shell.
The servo motor is reassembled and the feedback device(s) is aligned. Each data line from the encoder is checked including the commutation pulses, count pulses, and Z (or marker) pulse. If each signal from the encoder appears to be working properly, the technician will turn the shaft slowly and check the encoder count for error. If there is no error, the technician will then turn the shaft continuously (several thousand revolutions) and again check for errors.
The servo motor is again test run and checked for proper operation. This is accomplished by bringing the feedback from the servo motor being tested through a breakout box that outputs hall sensors (based on the commutation signals from the feedback device) to our test drive and fires our transistors. We run the servo motor to over its rated speed range and continue exercising it by reversing it until it gets to running temperature. RPMs, volts, and amperage are again checked and documented.
The servo motor is then painted and shipped in a foam encapsulated, double wall box to ensure the integrity of the repair when it gets back to the customer.
A packing slip showing what needed to be repaired, what may have caused the problem, and what we needed to do to do the repair is included with the repaired servo motor.