Acceleration & Deceleration Time Setting

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ax20
Posts: 9
Joined: Wed Jan 04, 2017 12:41 am

Acceleration & Deceleration Time Setting

Postby ax20 » Sun Jan 08, 2017 7:41 am

Dear OM Tech Support.

I appreciate the answer to my previous question on motor shaft considerations which is concise and illustrative. Actually in one of my project I have used a servo motor.

But another question I am going to ask is about control of ordinary BLDC motor, there are 3 questions:
1. What is the deceleration/accelration profile of BLDC motor?
2. What is the maximum/minimum decc/acc time setting possible?
3. Can I use more than one case for decc time/acc time? Such as differentiating of going from 2000-1000 rpm for deceleration and going from 2000-0 rpm with faster decc time for 2000-1000 rpm case and longer decc time for 2000-0 rpm case? Is there a limit of what case I can use?



Best regards,

om_tech_support_JS
Posts: 124
Joined: Tue May 10, 2016 4:48 pm

Re: Acceleration & Deceleration Time Setting

Postby om_tech_support_JS » Tue Jan 10, 2017 9:40 am

Hi ax20,

In regards to your questions, when setting the acceleration and deceleration time, you will create a trapezoidal motion profile similar to the example below:

Acceleration and Deceleration Motion Profile.png
Acceleration and Deceleration Motion Profile.png (26.5 KiB) Viewed 578 times


If your acceleration time and deceleration time take up the entire operating time, then you will create a triangular motion profile.

I have listed the acceleration and deceleration setting options for our current BLDC products below. Please note that these values are given at the rated speed and with no load. This means that the actual acceleration time and deceleration time may vary depending on the conditions of use (Speed, Load Inertia, Load Torque, etc.)

BMU: Internal Potentiometer (0.1 ~ 15 seconds) or Digital (0.0 ~ 15 seconds)
BLE: Internal Potentiometer (0.2 ~ 15 seconds) or Digital (0.2 ~ 15 seconds)
BLF: Digital (0.2 ~ 15 seconds)
BX2: Internal Potentiometer (0.1 ~ 30 seconds) or Digital (0.0 ~ 30 seconds)
BLH: Internal Potentiometer (0.5 ~ 10 seconds)


Lastly, the different series offer minor differences in the control of the acceleration and deceleration rates. For instance, the BMU series and BLH series offer 1 accel/decel potentiometer so both the acceleration and deceleration rates will be the same when using the potentiometer. However, for the BLE and BX2 series, there is one potentiometer for the acceleration and one for the deceleration so they could potentially be set differently. If you use the internal potentiometer to set the acceleration and deceleration rate, then it will be used for all speeds. However, if you use a digital setting, then you can set different acceleration and deceleration rates depending on the motion that you have selected. Therefore, by using a digital setting, and selecting between your motion profiles via the binary configuration of the M0 - M# inputs, you can achieve different acceleration and deceleration rates.

ax20
Posts: 9
Joined: Wed Jan 04, 2017 12:41 am

Re: Acceleration & Deceleration Time Setting

Postby ax20 » Fri Jan 13, 2017 1:58 am

Thank you for the answers,

Does it mean, setting accel/decel time will accel/decel TIME a constant value? Not a fixed accel/decel slope?

Best regards,

om_tech_support_JS
Posts: 124
Joined: Tue May 10, 2016 4:48 pm

Re: Acceleration & Deceleration Time Setting

Postby om_tech_support_JS » Mon Jan 16, 2017 11:57 am

Hi ax20,

The acceleration and deceleration is set by a specific time value. However, this time value is in relation to the rated speed of the product and with no load on the product. This means that the acceleration rate and deceleration rate (or the slope) will be used. Below is a graph from the BLF manual that shows setting the acceleration and deceleration time with two different set speeds.

Accerlation Time Based on Set Speed.png
Accerlation Time Based on Set Speed.png (154.96 KiB) Viewed 527 times


The rated speed value will depend on your product. For example, most BLH products have a rated speed of 2500 RPM. What this graph is showing is that if you set the speed lower than the rated speed, then your acceleration and deceleration time will actually be less than the set value of time. Therefore, if there is a specific time that you need to have for acceleration and deceleration, then you could use the given equation to better estimate the required set time.

Please note that this graph and equation do not take into consideration a load on the motor. When the motor is loaded, it has a larger inertia value to overcome. This inertia will cause the slope angle to be less, and will therefore result in a longer time to accelerate. With a loaded condition, you will need to test and adjust the acceleration and deceleration time to fit your application needs.


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