BLH series of motor SPEED PROBLEM

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gurcan2g
Posts: 5
Joined: Mon Oct 21, 2013 10:40 am

BLH series of motor SPEED PROBLEM

Hi,
I have an arm application with BLHM450KC motor. Lenght of the arm is 300mm with 10kg weight. The distance between centre of shaft and centre of gravity 100mm. The problem is when i want to lift the arm to opposite direction of mass the speed is ok but when i want to run the motor to the direction of mass speed is increasing. I'm referencing the speed from an external 0-5V supply. But speed is changing due to force on the arm. How can i solve this problem?thanks in advance.

om_tech_support_JT
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Re: BLH series of motor SPEED PROBLEM

Hi,

The BLH motor system has a built-in, self-contained closed-loop feedback and will only adjust its speed if it senses that it has been overloaded. Is your motor undersized? Could gravity play a part in overloading the motor in your application? Is the arm rotating horizontally or vertically?

If it's vertical, 10 kg x 0.3 m = 3 kg*m = 261 lb-in required for motor to rotate arm. We need atleast a BLH5100KC-100 (100W model with 100:1 gear ratio) to rotate your arm. A BLHM450KC motor with the highest gear ratio 200:1 will only output 141 lb-in rated torque.

If the above is true, then I can conclude that the motor is being overloaded. I would suggest upgrading to BLH5100KC-100 or BLH5100KC-200 (parallel shaft type). We have hollow shaft types available as well if you're interested.

For your current system, you can try to increase its acceleration/deceleration time to see if it improves performance a little bit, but there's not much else we can do unless you can lighten your load. Stepper motors might work better for arm rotations and it would provide holding torque.

Here are the specifications for the BLH5100KC-100:
PARALLEL SHAFT TYPE: http://catalog.orientalmotor.com/item/b ... 5100kc-100
HOLLOW SHAFT TYPE: http://catalog.orientalmotor.com/item/b ... 00kc-100fr

Here is the BLH SERIES CATALOG:
http://www.orientalmotor.com/products/p ... bl_blh.pdf

Here's our FREE ONLINE MOTOR SIZING CALCULATOR:
http://www.orientalmotor.com/support/motor-sizing.html

Please let me know if you have any questions.

gurcan2g
Posts: 5
Joined: Mon Oct 21, 2013 10:40 am

Re: BLH series of motor SPEED PROBLEM

Hi again,
I'm already using 100:1 gear ratio hallow shaft gearhead. I don't think,i have a problem with load.because motor resist to load very well in opposite direction of the shaft rotation. For example if i run the motor clockwise and load the shaft counter clockwise everything is ok. On the other hand, if i run the motor clockwise and load the shaft clockwise or "help the motor to rotate with my finger" the speed is increasing. When i'm trying to hold the motor when it's running,it's impossible to stop it, because the torque is very reliable and high. But there is a problem with the forcing same direction of the rotation of the motor.

om_tech_support_JT
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Re: BLH series of motor SPEED PROBLEM

Hi,

Thanks for the information.

Does the problem occur without load? Without arm?

How much does the speed increase if you "help" the motor shaft in the same direction that it's rotating? Does it increase speed forever? Does this problem occur during acceleration/deceleration or at constant speed? Have you received any driver alarms? How many blinks?

I just did a test with a BLH series motor and the speed would return to set speed no matter if I try to slow down or "help" the motor then letting the shaft free before any driver alarms occur (5 seconds). I cannot simulate your issue here. The BLH450KC-100FR model can handle 141 lb-in from 1~25 RPM and about 34,000 oz-in^2 of load inertia (3000 oz-in^2 if using instantaneous stop function). I still believe going with a bigger motor with more torque would resolve your problem, but I cannot be sure if I don't know your torque and inertia requirements.

Have you tried increasing the acceleration/deceleration time? Does it help?

gurcan2g
Posts: 5
Joined: Mon Oct 21, 2013 10:40 am

Re: BLH series of motor SPEED PROBLEM

Does the problem occur without load? Without arm?
"I haven't tried without load yet because i need to hold the shaft with something (with my hand or something).But speed is ok and i have no problem without load."

"Vertical. I didn't calculate the interia."

How much does the speed increase if you "help" the motor shaft in the same direction that it's rotating? Does it increase speed forever? Does this problem occur during acceleration/deceleration or at constant speed? Have you received any driver alarms? How many blinks?
"My application is just like a clock watch. While running in clockwise,Speed increases from 12 o'clock 5 o'clock and then gets normal after 5 o'clock to 12 o'clock. Speed is increasing like the arm is falling freely and there is no alarm on the driver. In every situation problem is the same(acc,dec,cons)."

I just did a test with a BLH series motor and the speed would return to set speed no matter if I try to slow down or "help" the motor then letting the shaft free before any driver alarms occur (5 seconds). I cannot simulate your issue here. The BLH450KC-100FR model can handle 141 lb-in from 1~25 RPM and about 34,000 oz-in^2 of load inertia (3000 oz-in^2 if using instantaneous stop function). I still believe going with a bigger motor with more torque would resolve your problem, but I cannot be sure if I don't know your torque and inertia requirements.

Have you tried increasing the acceleration/deceleration time? Does it help?
"I have tried increasing time but it was all the same."

"If it is possible,is changing direction with high frequency can slow down the motor? Of course with 10ms limit.
I live in Turkey and getting a new set of motor last about 2 or 3 months at least.This is too long for me. I'm aware of that maybe i have choosen a wrong motor but the torque of the motor against to load while lifting is very well and this leaves a doubt in my mind."

om_tech_support_JT
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Re: BLH series of motor SPEED PROBLEM

I may have overestimated your torque. The 3 kg*m or 261 lb-in torque requirement was calculated for an 300mm long arm with the motor mounted on one end, and the 10 kg load mounted on the other end. I did not consider your 100mm distance from center of rotation to center of gravity. So actually that's 10kg x 0.1m = 1 kg*m = 86.8 lb-in; not 10kg x 0.3m = 3 kg*m = 261 lb-in. The BLH450KC-100FR provides 141 lb-in so it's sufficient.

If you have a vertical arm orientated like a wall clock, and the motor speeds up from the 12 o' clock position to 5 o' clock, that still tells me that gravity is causing the load to fall quicker thus increasing its speed. If the motor is allowed to catch up with its speed within 5 seconds, then the driver wouldn't generate an overload alarm. I still think a bigger gearmotor would help since more torque would help stablize the speed better and cancel out the gravity effect. A higher gear ratio would also help because the higher gear ratio would provide more friction torque to help stop the load from dropping. You should also look into stepper motors perhaps for your next design. They're better for vertical applications.

A simple test you can do to prove my theory is to turn your arm from a vertical orientation to a horizontal orientation and see if the problem is still there. Or you can try to run it CCW and see if the speed now increases from 12 to 7 o' clock. The constant back EMF regeneration from the motor being backdriven by gravity constantly is also not good for the motor driver. We would recommend that you avoid it as much as possible since it may damage the driver.

om_tech_support_JT
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Re: BLH series of motor SPEED PROBLEM

I should also mention that stepper motors also handle inertia better.

gurcan2g
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Joined: Mon Oct 21, 2013 10:40 am

Re: BLH series of motor SPEED PROBLEM

i will give a try to a bigger gear ratio and think about using a stepper motor.thank you very much for your advices and help.

om_tech_support_JT
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Re: BLH series of motor SPEED PROBLEM

OK. Feel free to update us with your results.

gurcan2g
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Joined: Mon Oct 21, 2013 10:40 am

Re: BLH series of motor SPEED PROBLEM

Hi again,
I think i found out the solution. The problem is that BLH series of motor drivers are 2 quadrant motor driver. But in my application,i need a 4 quadrant motor driver. So it will solve my problem that using 4 quadrant driver because as you said theese driver works only in overload situations. But in underloaded applications i need a 4 quadrant type,i think. If you have a model of this,would you suggest me the type of driver?
Thanks

om_tech_support_JT
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Joined: Fri Mar 12, 2010 2:59 pm
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Re: BLH series of motor SPEED PROBLEM

Unfortunately, we only offer one type driver for our BLH series brushless motor systems. The 4-quadrant driver seems to be typically used for servo systems, and it handles back EMF well from a back-driven motor. We still think that gravity is the cause of your issues. My recommendations would stay the same.

I would suggest an AR series hybrid stepper/servo system, and use a "regeneration unit" (optional accessory). The RGB100 regeneration unit is designed to absorb the back EMF that could be generated from a back-driven motor, then dissipate it as heat.

An AR package model that can output atleast 200 lb-in holding torque would be sufficient. Something like the following:
[ AR98MA-PS50-3 ]
http://catalog.orientalmotor.com/item/a ... 8ma-ps50-3
-an electromagnetic brake is included to hold the arm in place when power is removed.
-a pulse input type driver is included. We have other control options available.

The maximum holding torque spec needs to be double of what you need since our driver cuts back 50% of the maximum holding torque when the motor is at an energized, holding state. This is for reducing motor temperature when the motor is not moving, and is common with stepper drivers.

Remember to add [ RGB100 ] to your order if you decide to try this.