Steps in Running a Motor

The steps in running a supported motor are simple and quick. The following sections describe in detail the steps involved.

Drive Considerations

The AMC drives will last a long time if care is take when test running motors. Using these drives in a test environment requires extra care to insure that the drive is not inadvertently damaged. Use the check list below to help insure that the drive is not exposed to hazards that will shorten its life.

DO-

1. Ensure that the dipswitch settings are correct according to this Introduction article when installing a replacement drive (especially important if the drive was purchased direct from AMC). Incorrect dipswitch settings can result in loss of speed control and other problems. Contact support at Mitchell Electronics, Inc., if you have questions.

2. Remove AC power from the drive until the motor is completely connected, debugged and ready to run. It is much more difficult to damage the drive if it is not under power.

3. Ensure that the armature phase leads are connected tightly to the motor power pins. If they momentarily lose connection to the motor pin, arcing will occur which produces high voltages that may be damaging to the drive. If a lead loses connection completely, the motor will probably stall, and high damaging currents to the drive may result.

4. Ensure that the feedback leads are connected correctly and tightly to the motor feedback and TI-3000 (use the correct test cable if possible). If the feedback signals are momentarily lost, the motor will probably stall, and high damaging currents to the drive may result.

5. Always perform the DEBUG procedure before running the motor to verify that the feedback device is working properly.

6. Always perform the DEBUG procedure before running the motor to verify that the feedback device is aligned correctly. An incorrectly aligned motor will draw excessive currents and the generated voltage will not be phase correctly with the drive voltage. Besides, a test run with an incorrectly aligned motor provides no useful information.

DON'T-

1. Run a motor that is not physically secured. Instantaneous torque can jerk the motor violently which could result in damage or injury as well as losing connections to the motor.

2. Allow the armature power leads to touch each other or other conducting objects(metal bench, etc.)when the drive is powered up. Even when the drive is disabled (GREEN LED OFF and RED LED ON), power leads shorting to ground or each other can be damaging to the drive. 

3. Remove feedback or power leads when the drive is powered (especially if it is running a motor).

4. Power down the drive while a motor is running except in emergencies. The generated voltage from the motor can damage the drive.

5. Manually rotate the motor at a fast rate with the armature power leads connected between the motor and drive. The generated voltage can damage the drive.

6. Run the motor if the DEBUG procedure did not indicate correct feedback operation and alignment.

Motor Feedback Connection

The connection of the motor/encoder to the TI-3000JX system is relatively simple. The U, V, and W armature leads must be connected to the designated U, V, and W current outputs of the servo amplifier. Resolvers connect to the TI-3000JX via the J12 7 pin terminal block connector while the encoder or hall effect outputs must be connected to theJ1 14 pin and J2 12pin terminal block connectors. Fanuc serial encoders will need to connect only to J1.The Fanuc encoders can be connected using pre-made cables from Mitchell Electronics, Inc. These cables are described in section 2.6.Customers who have purchased the TI-5000JX encoder test system will already have many of these cables. The TI-3000JX and TI-5000JX systems are designed to share the same cables.

Hall Feedback Connections

In the case of generic 3 phase commutation pulses, the cable will often be user fabricated. The connections should be as follows:

Please note that the TI-3000JX provides a 5 volt supply for powering the encoder and/or Hall effect pickups. Some encoders and Hall effects specify higher voltages. In general, the specified voltage should always be used for an encoder. However, Hall effect pickups are often not very sensitive to power supply voltage range. It is not uncommon to see Hall effects that are specified for +12 or +15 volts that will work fine at +5 volts. This is a judgment call that you should make carefully, but using the TI-3000JX 5 volt output is convenient and can save time. If you have a variable voltage bench supply, you might try running the voltage down to 3 or 4 volts. If the supply can get down to4 volts and still produce good Hall effect pulses with proper phasing, then you can assume that +5 volts will work for them.

If the commutation is 60 degrees, it is very important that you assign the complemented line to be the Hwu line. For 120 degree motors, you may assign lines any way that you want as long as they agree with the armature phases.

Noise Considerations

Due consideration must be given to minimizing the electrical noise picked up by the feedback device. Amplifiers produce the armature excitation voltages and currents by pulse width modulation (PWM). PWM isa method of very efficiently adjusting an average voltage by the relative amounts of ON and OFF time. For several reasons, it is usually best to make the PWM frequency fairly high (above the audible range).Frequencies from 30 KHz. to 100 KHz. are common. An unfortunate side effect of this is that the PWM is a very efficient electrical noise generator. If too much PWM noise is picked up by the feedback circuit, it can corrupt the feedback signal which in turn can cause the motor to run poorly under test. Excessive audible clicking and sounds of rough speed characteristics (not a smooth sound of a constant speed) are symptoms of excessive electrical noise pickup. The resolvers seem to be most affected by noise pickup. You can connect a scope to the returning cosine and sine signals via the TI-3011 resolver breakout board test-points to see how much noise pickup is occurring. Compare the scope trace with and without power applied to the amplifier. 

Several basic steps can be taken to reduce the noise pickup:

1. Route the armature conductors and the feedback conductors as far apart from each other as possible.

2. Keep the armature conductors together rather than lying loosely apart. Twisting is better than loose conductors. Multi-conductor cable is better yet, and shielded multi-conductor cable is best.

3. Connect a ground conductor from the motor case to the amplifier case. Ideally this could be the shield of a shielded cable used for the armature conductors. The TI-3007 Quick Change board has a frame ground terminal connected to the shield. Make sure that the amplifier is connected to a good earth ground such as the safety ground system of the electrical system (where the 3rdprong of an appliance plug connects).

4. Keep the feedback conductors together rather than lying loosely apart. Twisting is better than loose conductors. Multi-conductor cable is better yet, and shielded multi-conductor cable is best.

5. If shielded cable is used, it can be connected to the case of the feedback device and to the ground pin of the TI-3000JX. This seems to be especially helpful in reducing resolver noise pickup.

Normally some combination of the above steps will reduce the noise to an acceptable level. The higher the armature currents, the worse the noise problem is likely to be. Therefore, less attention to noise will be necessary for smaller motors under no load than larger motors perhaps under some load.