That stepper driver’s high pitch squealing is driving me nuts! Well, it has to drive you somehow as after all it is a “driver”, right? Well, nuts should not be it. It should drive your stepper motor and be done with it. But what if by nature stepper motors are noise and it is just a matter of learning to live with it?
Chances are you are not about to buy into such a lifestyle. You have heard quiet stepper drives and you want one to! So if you are experiencing some undesirable high pitch squealing from your stepper motor driver and are in need of reducing this horrendous form of ear-torture, feel free to check out these easy steps:
Where does it come from? Why can I hear it? Shouldn’t this motor be completely silent? If it were disabled it would be silent. But when energized, it is just not possible. Especially when we are regulating the winding currents by chopping them into submission. Current chopping is the preferred method of driving steppers nowadays. It is way much more efficient than having a humonghous resistor to limit the current, occupies less space, cost less and generates less heat. It is just the way to go.
Solution #1: Increase Switching Frequency
The current chopper circuitry will most likely offer you some way in which you can increase the switching frequency. For example, in the DRV8811 this is achieved by changing the R and C components at the RCx pins. These two components will change the TIME_OFF portion of the current regulation period. The smaller the TIME_OFF, the smaller the total current regulation period which is the same as the higher the frequency. Hence, you will want to decrease the R component to some value in which your frequency is considerably higher than 20 KHz.
Solution #2: Decrease Stepper Current
Decreasing the winding current also decreases the audible noise to some extent. This venue will work for both during run time as well as holding torque instances. During run time, the less current you use, the less vibration. However, it also means the less torque. So decreasing current will work up to some point. If you decrease too much, you may start loosing steps and this is a big NO NO when it comes to stepper driving. Since you are operating the motor in open loop, you must ensure the right amount of current is supplied at all times.
Solution #3: Use Slow Decay Versus Fast or Mixed Decay
When possible, you will want to operate your motor on slow decay current recirculation mode, instead of fast or mixed decay. This is especially true if you are actuating your motor with full step commutation. Other than decreased noise, as the current ripple is the smallest possible, you will also obtain the most efficient usage of your H Bridge. For example, under slow decay you will get better torque response due to the fact that average current is larger with this mode than with the higher current ripple observed while on fast decay mode.
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