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Motor Drivers Forum
Bipolar stepper motor- mainly: positioning- which driver?
I need a precise positioning a bipolar stepper motor 8V, 0.8A by a (probably) microcontroller (0-360 degrees) with 0,2-1,8 degree angle precision (it would be more, but then i will need to use more complex mechanical system). The best thing for desegner (and uC which will responsible for other operations) would be a controller which receive a directrion and angle, move motor to specified position and hold it (in ~"low power consumption mode") since controller hasn' t information about next operation.
1. There is no chip like this so... what controller is the best to achieve that?
2. Do you think that open loop system would be sufficient? Maybe optical encoder will be helpful?
3. I have found: DRV8834 and DRV8811 drivers and it should be very useful. What do you think about it? Maybe I will order some samples for testing.
There is a fair number of options I can mention. These are in just numerical order, but not in order of better fit to this application:
DRV8811 (Up to 8 degrees of microstepping)
DRV8812 (You will need a microcontroller to do microstepping)
DRV8813 (You will need a microcontroller to do microstepping)
DRV8818 (Up to 8 degrees of microstepping)
DRV8821 (Up to 8 degrees of microstepping)
DRV8824 (Up to 32 degrees of microstepping)
DRV8825 (Up to 32 degrees of microstepping)
DRV8828 (you will need two of these and a microcontroller to do microstepping)
DRV8829 (you will need two of these and a microcontroller to do microstepping)
DRV8833 (You will need a microcontroller to cause full step commutation)
DRV8834 (Up to 32 degrees of microstepping in Internal Indexer Mode, infinite microstepping in external indexer mode)
There are other parts which can also be used to drive steppers, but why make your life harder? Let me tell you how I would do this and why:
If the application voltage will never go over 10.8V and the peak current will not increase more than 1 or 2A, then the DRV8834 is definitely the best option. This device can do excellent microstepping and it should be able to deliver your accuracy and precision requirements. As stated above, it is the best of both worlds, as it can do either internal indexer microstepping with up to 32 degrees, or it can use external microcontroller microstepping techniques. I have coded up to 512 degrees of microstepping and the result is simply astounding, with the best motion quality you could hope for. Thanks to dynamic TBLANK, the zero crossing distortion, and torque ripple, are minimized considerably.
You will need to couple this driver chip with a microcontroller, but that is pretty much standard operation nowadays. I use different MSP430's to do all of my stepper based applications and they are all more than capable to tackle these applications. Timers can be used to generate the STEP pulse and the different GPIO's and interrupt sources can be used to gain some form of feedback, whether digital or analog. The microcontroller would keep track of the shaft angle and move according to the command from this reference point. Commands can be issued via UART, I2C, SPI or even a potentiometer.
The stepper will need to be homed to angle zero and then pulses can be issued as to move the shaft to the desired position. For this homing, there is no need for a shaft encoder. A flag and optical sensor should be more than enough.
If you need the shaft to protect the commanded position even as load changes, you will need a shaft encoder or a resolver to transform the stepper into a servo application. This is not typical stepper operation as the great majority of applications using steppers will resort to the open loop advantages of this motor topology. However, using the stepper as a servo is quite doable and some people implement drives of this sort.
Whether the open loop will be sufficient or not depends on whether the external load can be such as to move the shaft away from position. Once that happens, further angle accuracy would be compromised and the motor would need to be re-homed. Unfortunately, you would not know that it happened until you can corroborate that the home position is still on the angle in which the home position was (i.e. if you find that the home transition is now at angle 2 or -358, then you know steps were lost). If enough current is present, however, this should not happen. Each application will speak for itself, though, so you will need to decide whether the homing flag or the shaft encoder is best.
Hope the info helps. Best regards,
I didn't expect so professional reply. Thank you very much for fast and very helpful answer.
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