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MCF8316A: High-side brake and align brake

Le Duc
Prodigy 50 points
Part Number: MCF8316A
Other Parts Discussed in Thread: MCT8316Z,

Tool/software:

Hello expert
I am researching the MCF8316A for my motor control project. The motor has a maximum torque of 11mNm and a maximum acceleration of 204,000 rad/s^2. With MCF8316A, Can I control the motor to rotate 17 degrees in 1.8ms and then brake the motor with high side braking and can the motor stop before an angle of 19 degrees? . Is the align brake function suitable for my needs?

Note : J_total = 1.99*10^(-8)

Thank you expert. Have a nice day.

  • 0
    TI__Genius 9220 points

    Hi Le Duc,

    The MCF8316A integrates a sensorless FOC algorithm that's ideal for speed control applications. Though doable, it'd be more difficult to use this driver to implement position control applications.

    You'd most likely need to have an encoder mounted on the motor and use an external microcontroller to process the encoder signal and implement position control loop.

    The align brake function on the MCF8316A applies a constant vector field and can be used to brake and hold the motor at a specific electrical commutation angle. However, on motors that have 2 or more motor pole pairs, the same electrical align angle can result in the rotor shaft being held in multiple different mechanical angles.

    Basically, the MCF8316A is not able to monitor absolute angular position of the rotor without sensors, and therefore you'll need the external encoder for that.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 50 points

    Hello expert.

    My project uses a 3-phase 2-pole BLDC seri FAULHABER 1628T024B motor and has a analog hall sensor. For my application , i need to control motor move from angle 0 degree to angle 17 degree in less than 2ms then use the brake to stop it before the 19 degree angle .The allowed angle error is 0.5 degrees. So, is the mcf8316a driver suitable for my application?

    Thanks expert and have a nice day !

  • 0 in reply to Le Duc
    TI__Genius 9220 points

    Hi Le Duc,

    As I mentioned above, for precise angular position control, you'll need to use a position encoder that can accurately keep track of the rotor's absolute position.

    The FAULHABER 1628T024B motor contains hall sensors that are used for sensored commutation algorithm (on devices like the MCT8316Z that has sensored commutation algorithm).

    The MCF8316A uses sensorless FOC algorithm, which would not be able to utilize the hall sensor signals. You could still drive the motor with MCF8316A only using the 3 phase wires, and simply ignore the hall sensors.

    Regardless, for precise angular position control, you'll need to use a position encoder that can give you 0.5 degrees resolution, and implement position control loop on an external microcontroller.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 50 points

    My application uses an external ADC to read values ​​from an analog Hall sensor. The MCU then converts these values ​​into actual angles and performs position control by driving the MCF8316A at its highest speed. When the MCU reads that the actual angle matches the requested angle, it activates the high side brake function of the MCF8316A.
    For example, my motor has J_total = 1.99*10^(-8) and maximum motor speed = 2860 rpm.When power is turned on, the motor will be aligned at 0 degree angle. And when the external trigger is activated. I need to control the motor from a 0 degree angle to a 17 degree angle in less than 2ms then use the brake to stop before the 19 degree angle.. Can MCF8316A control that? . And do you have any suggestions on choosing a suitable MCU?

  • +1 in reply to Le Duc
    TI__Genius 9220 points

    Hi Le Duc,

    Assuming your position estimator based on analog hall sensors is accurate enough, then yes, you could potentially achieve position control using the MCF8316A's align brake functionality to apply stationary holding torque.

    You would configure [ALIGN_BRAKE_ANGLE_SEL] to "Use last commutation angle before entering align braking". And the MCU would simply command the MCF8316 to BRAKE when the target rotor angle is reached. Depending on the load and speed of the motor, if you experience overshoot and wobble, you might need to implement some form of deceleration as the rotor angle approaches your target angle.

    I'm not sure what your ADC resolution/accuracy requirements are, but you might even consider MCUs that have built-in ADC. The MSPM0 microcontrollers could be a good place to start exploring possible options.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 200 points

    Hi Eric, I'm Duc's coworker. Thanks for your answer.


    As you know, we have limited tolerance for position is 0.5 degrees. This tolerance includes error from reading ADC of MCU, the time for processing of ADC and the time of braking from MCF8316. We need to have the estimate for this to review the feasible of this method.

    With MCF8316, we are concerned about the time of braking, details: mechanism , acceleration value with our conditionals about motor and load Duc gave. We appriciate so much if you could help us to have this estimated time.

    Thanks very much

  • 0 in reply to Eric Chen
    Prodigy 50 points

    Hi expert !

    I have read the data about MCF8316A. In my application, the MCF8316A must always be ready to operate without entering standby or sleep mode. I can provide both the Brake Pedal signal at 100% duty cycle and the Brake Pedal signal high to use the algin brake mode which keeps the motor at a fixed angle and then when the Pedal signal Apply the brake at a low level, can the engine react immediately without delay? . How to configure like that?

  • 0 in reply to Le Duc
    TI__Genius 9220 points

    Hi Le Duc,

    Could you please help clarify what end application/product are you designing for? Does the motor have high load/inertia and do you need a lot of holding-torque to keep the rotor at a specific position? The align brake of the sensorless FOC algorithm will apply some holding torque, but it will not be very strong.

    The MCF8316A will enter standby based on the condition in this table:

    And it takes 6ms for the device to start driving the motor after exiting standby.

    You could simply keep the SPEED pin voltage above the standby conditions to prevent the device from entering standby, and toggle on/off the brake pin to stop/start the motor.

    I did a crude test on a motor using the MCF8316AEVM and was able to get it to spin and stop at different angles using a Brake switch. I had to disable the ISD functionality in the device in order to get the device to immediately start spinning the motor consistently every time BRAKE pin is turn off.

    However, since align brake doesn't apply a strong torque when the rotor is aligned (the align torque will only be strongest when rotor is 90 degrees offset from the align angle), it was relatively easy for me to manually move the rotor away from the align angle using my hand. 

    In terms of angle accuracy, the Align Brake feature can simply be configured use the last commutation angle as the align brake angle. Unfortunately, sensorless FOC is not good at spinning the motor at 0 or low speed, so if you are doing minor angular adjustments, the device will most likely be spinning the motor in Open Loop (aka blind commutation) instead of Closed Loop commutation.

    At the end of the day, I would recommend obtaining the MCF8316AEVM and do a prototype test with your position control, since the feasibility of using MCF8316A is heavily dependent on your application requirements and other factors.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 50 points

    Our application is to develop a new version of the spectrometer shutter controller. The motor in use meets our requirements. However, in the new version we want to use MCF8316A combined with MCU and analog Hall sensor to control the shutter opening/closing.
    You said: "The sensorless FOC algorithm's alignment brake will apply some holding torque but it won't be very strong." I want to know how the holding torque of the algin brake mode is calculated and set? and "not very strong" means how much holding torque can the MCF8316A provide? In addition, I hope the expert can explain to me in more detail about the high side brake and low side brake modes. I need to stop the shutter at an angle of 17 degrees and must stop at an angle of 19 degrees and the shutter is not allowed to drift below 17 degrees. Which braking mode is right for me?
    Note :
          Max torque of motor = 11mMm
          J_total ( motor + shutter ) = 1.99*10^(-8) kg.m^2
          Torque constant K_m = 7.08mMm/A

    Thank you expert !

  • 0 in reply to Le Duc
    TI__Mastermind 26826 points

    Hi Le Duc,

    Thanks for your response! Eric is out of office today, but should be able to get back to you by the end of the week.

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    Prodigy 50 points

    Hello Anthony Lodi, do you have any new updates for my topic?

  • 0 in reply to Le Duc
    TI__Genius 9220 points

    Hi Le Duc,

    The reason I said Align Brake doesn't apply strong holding torque is because the device simply applies a DC current through the 3 motor phases, which generates a static magnetic align vector field. When the rotor is perfectly aligned with the Align Brake vector, the applied torque to the rotor is technically 0. And if the rotor starts to deviate away from the align brake angle, then the applied torque will slowly increase up to the maximum torque when the rotor is 90 degrees away from the align vector. The applied DC align current/torque is configured using the [ALIGN_OR_SLOW_CURRENT_ILIMIT] register.

    Align brake wouldn't be very effective if there is significant and dynamically changing load to the rotor at any given position, because when the rotor is very close to the aligned position, very small portion of the align current is actually applying torque. Like I mentioned earlier, it's very easy for me to manually move the rotor away from the align position. Then the further I move the rotor, the more I can feel the torque from the align brake.

    A true 0 speed max torque position control algorithm is able to apply max torque against the rotor even when the rotor is only slightly deviated from the target position. This type of algorithm requires the motor commutation algorithm to be able to have rotor position feedback even at zero/low speeds, and MCF8316A's integrated sensorless FOC would not be able to achieve this. You'd need to implement your own sensored FOC commutation algorithm that can apply max torque at zero/low speed.

    So to answer whether align brake is even feasible for your application, you'll need to figure out how much external load/force would be trying to move the rotor away from the aligned angle, and perhaps do some prototype testing using the MCF8316AEVM to find out whether align brake has sufficient precision and holding torque to keep the rotor at the desired position.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 50 points

    Hi expert

    With our application the motor will not be subjected to any external force trying to move the motor. The load values ​​are fixed. I would like to know if there is a way to stop and hold the motor at a certain position as quickly as possible

  • 0 in reply to Le Duc
    TI__Mastermind 23832 points

    Hi Le Duc,

    Eric is out of office, our team will respond to your question by end of this week.

    We need to look back this thread and understand the problem and status, kindly provide a daytime.

    Thanks and Best Regards,

    Venkatadri S