The issue of wiring the hall sensors on brushless servo motors often arises here in the Galil Applications Department. This is due to a lack of standardization in hall wire labeling between, and often within, motor manufacturers, hall designations, and labels. Often this results in confusion as to which hall phase lead on the motor corresponds to which hall phase connection on the servo amplifier. For example, a motor's hall leads may be labeled as halls U, V and W and the amplifier hall connections may be labeled as halls A, B and C. Fortunately there is a straight forward way to decipher the wiring of your hall sensors using a system of trial and error.
The first step to wiring the hall sensors on any motor is to figure out how many possible wiring combinations there are. For a 3 phase motor there will be 3 hall leads. Some hall sensors will supply a positive and negative hall signal (meaning there will be 2 wires per hall sensor), however Galil servo amplifiers only require the positive lead for proper commutation.
1)
Using good-old factorial (the ! sign on your calculator) you can figure the number of combinations for any number of unknowns, or in this case wire combinations, based on number of wires. For a 3 phase motor with 3 hall sensors there are 3 leads meaning 3 unknowns. Calculating the factorial of 3, or 3!, we find that there are 6 possible combinations of hall connections. These combinations are listed in the table below.
|
Table of Hall Combinations |
|||
|
Amplifier Connection |
A |
B |
C |
|
Hall Connection |
1 |
2 |
3 |
|
" " |
1 |
3 |
2 |
|
" " |
2 |
1 |
3 |
|
" " |
2 |
3 |
1 |
|
" " |
3 |
1 |
2 |
|
" " |
3 |
2 |
1 |
2)
After finding all possible wiring combinations the next thing to do is to turn off the feedback to the controller. This can be done by turning the P, I and D gains off or setting KIn=0, KPn=0 and KDn=0, where n is the axis to which the motor is being wired.
3)
Next you will need to provide a motor command signal to the amplifier using the OFn= command. A good value to start with is .75V or OFn=.75. The magnitude of the motor command signal is important because the motor command signal has to be large enough to provide ample torque to overcome any friction within the motor and also spin the motor slow enough to show any inconsistencies in commutation. And here in the Apps department though we have found that a motor command signal of .75V is the best place to start.
After you issue this command query the velocity of the motor with the TV command and note this value.
4)
Next, issue the same OFn command to the axis, but in the negative direction. For instance if you issued an OFn=.75 in step 3 issue an OFn=-.75 in this step and query the velocity again.
**It is okay if the motor doesn't spin, or spins erratically. This is an indication of an incorrect wiring scheme, immediately eliminating one possibility. **
5)
Re-wire the hall sensors to the next combination listed in step 1 and repeat processes 2-4. A sample table of velocities during this test can be seen below.
|
|
Table of Hall Combinations |
OFn=.75 |
OFn=-.75 |
||
|
Amplifier Connection |
A |
B |
C |
Velocity |
|
|
Hall Connection |
1 |
2 |
3 |
16235 |
-35621 |
|
" " |
1 |
3 |
2 |
0 |
0 |
|
" " |
2 |
1 |
3 |
25617 |
-26100 |
|
" " |
2 |
3 |
1 |
340 |
0 |
|
" " |
3 |
1 |
2 |
4862 |
-10586 |
|
" " |
3 |
2 |
1 |
0 |
-74562 |
6)
The correct combination will be the one where the velocities in both directions for a given wiring combination are closest in magnitude. Wire the hall sensors in this combination. In the table above the proper wiring combination would be; 2 1 3. If there is no conclusive results from this test, try raising or lowering the OFn command issued.
After that you can turn your gains (KI, KP and KD) back on, verify feedback, motor polarity and you should be properly servo'ed.