## Maximum Permissible Inertia

Discuss AC Induction motors, Reversible motors, Synchronous motors, Low-Speed Synchronous motors, Torque motors, Gearheads, Brake Packs and related Accessories here.
arifoyong
Posts: 5
Joined: Tue Apr 05, 2011 3:55 am

### Maximum Permissible Inertia

Hi,

I am designing a system for horizontal reciprocating motion in sieving operation.
The sieving mechanism will be supported by LM Guide, and it is connected to a motor via a bar.
The whole system is similar to a slider crank mechanism but in horizontal position.

The size of the system is 800mm x 400mm, with a weight of 12kg.
Based on the torque and speed requirement, 4RK25GN - 4GN3K should be sufficient, (i am assuming the fricition coefficient of the LM guide is very low).
However, I found out in Oriental Motor catalogue, that there is a maximum permissible inertia for motor and gear head.
I did a rough calculation on the inertia of a 12kg rectangular box, and the results actually exceed the maximum permissible inertia for the selected motor and gear head.

My question is, how does this inertia affect my system, because theoretically I should have enough torque.
Will produce jerking motion??

omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

### Re: Maximum Permissible Inertia

HI.

With an AC motor, if the inertia is too large, the motor may not be able to start correctly. Since there is no real acceleration per se for an AC motor, we need to make sure that inertia isn't too large.

When the AC power is applied to the motor windings, a magnetic field is "induced" on the rotor. The magnetic field of the rotor then tries to "catch up" to the varying magnetic field produced by the AC power in the motor windings. In reality, the rotor position is always lagging behind the field in the stator (motor windings). If the inertia is too large, this lag becomes too big for the rotor to catch up, causing the motor to not start or stall.

Just to make sure, what value for inertia did you some up with?
Oriental Motor Product Forum Support
forum@orientalmotor.com

arifoyong
Posts: 5
Joined: Tue Apr 05, 2011 3:55 am

### Re: Maximum Permissible Inertia

I just did some rough calculations with J = 1/12 * mass * (w^2 + l^2).
So with mass = 12 kg, w = 400mm, l = 800mm, I got my inertia of 0.8 kg. m^2
The mass and the size are actually bigger than the actual design, so I still have some safety factor there.

Maximum permissible inertia for frame 60 motor is 0.062e-4 kg.m^2. So I wonder if my calculation is wrong.

However, the reciprocating motion is needed to sieve some chips and how the motor starts is not really a concern for me, as long as it can start and drive the mechanism. But during the sieving process, I can't have some jerking movement.
Thanks for your help

omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

### Re: Maximum Permissible Inertia

Two things:

1) According to your calculations, your J load is 0.8KG-m^2. For a 4GN3K gearhead, the table on page A-17 of the catalog says that the maximum permiisible J at the motor shaft is 0.31e-04 KG-m^2.

So, if you take your load inertia of 0.8 and divide it by the gear ratio squared (3 * 3 = 9), you get 0.09 KG-m^2 at the motor shaft. 0.09 is < 0.31, so you should be OK!!

2) What is the duty cycle of this application? A reversible motor, like you have chosen, has a 30 minute duty rating. This means 30 minutes ON followed by 30 minutes OFF. Will this motor be running for more than 30 minutes at a time? If so and the mot0or only needs to run in one direction, you should consider using an induction motor.

What do you think?
Oriental Motor Product Forum Support
forum@orientalmotor.com

arifoyong
Posts: 5
Joined: Tue Apr 05, 2011 3:55 am

### Re: Maximum Permissible Inertia

Hi,

My calculated J is 0.8 kg.m2, so with gear head I can get 0.09.
But the maximum permissible inertia is 0.31e-4 which is bigger than 0.09.

My duty cycle is only 5 min at most, but I need the reversed direction.
Based on experiment, sieving action with 2 directional action will give better result.

omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

### Re: Maximum Permissible Inertia

Sorry about forgetting about the 10^-4 factor.

What will you try to do?
Oriental Motor Product Forum Support
forum@orientalmotor.com

arifoyong
Posts: 5
Joined: Tue Apr 05, 2011 3:55 am

### Re: Maximum Permissible Inertia

Hi,

I saw a similar application, probably with half of my size.
Assuming, it's 5kg and 400x200mm, J = 0.2 * 0.4 * 5 = 0.083 kg.m^2
At 0.31e-4, the permissible inertia is much lesser.
However, the system is working fine.

But, actually the whole system is supported by LM guide.
The motor is just providing the reciprocating motion.
So, my suspect is that because the system is not fully supported by the motor, the inertia at the motor shaft is much lesser.
Hopefully, my guess is correct.

My initial design is similar. I'll be using LM guide to support the whole system
The motor is used to drive the reciprocating motion by means of a link with bearing.

omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

### Re: Maximum Permissible Inertia

Please keep us updated.
Oriental Motor Product Forum Support
forum@orientalmotor.com

arifoyong
Posts: 5
Joined: Tue Apr 05, 2011 3:55 am

### Re: Maximum Permissible Inertia

Btw, I am also looking to use reversible motor with electromagnetic brake type(it's for another application).
In addition, I need the speed controller also.

Based on torque requirement, I need 5RK60GE-CW2ME type
In the catalogue for ES01/ES02, to I need to add 'R' in the model no in order to specify the controller.
However, I could not find any motor with model no 5RK60RGE.
Instead, I found 5RK60RGU.

My question is, what is the difference between GE type pinion and GU type.
If I need reversible motor with electromagnetic brake type, can I use 5RK60RGU??
or is there any model such as 5RK60RGE?

Thanks

om_tech_support_JT
Posts: 1058
Joined: Fri Mar 12, 2010 2:59 pm
Location: Torrance, CA
Contact:

### Re: Maximum Permissible Inertia

Hi,

GE and GU in our motor and gearhead model numbers designate what type of motor pinion shaft and mating gears we use. Motors with "GE" in the model numbers are designed to be attached to gearhead model numbers that also include "GE". A "GU" type motor will not be compatible with a "GE" type gearhead. There are also benefits with the newer "GE" type gearheads. These offer RoHS compliancy and twice the expected life (10,000 continuous hours) when compared to "GU" type gearheads; due to improvements we made in the bearing and gears. The newer "GE" type motors also offer RoHS compliancy and twice the expected life when compared to "GU" type motors; due to the improvements we made on bearing grease.

If you need a reversible motor with electromagnetic brake, I would suggest using the newer 5RK60GE-CW2ME motor along with a newer 5GE[ ]SA type gearhead for the benefits I've listed above.

Unfortunately, we do not offer speed control type electromagnetic brake AC induction motors. However, since we offer a 3ph version of the motor you picked out, we can use one of our inverters to control its speed. Please see my recommendation below.

[ FE100A, 5IK90GE-SW2 ] plus a list of compatible gearheads
http://catalog.orientalmotor.com/keywor ... IK90GE-SW2

You will have to disengage the brake externally of the FE inverter by supplying voltage directly into our brake leads.

Let us know if you have any more questions.

appsmartvn
Posts: 2
Joined: Wed Nov 23, 2016 9:53 pm

### Re: Maximum Permissible Inertia

My calculated J is 0.8 kg.m2, so with gear head I can get 0.09.

Return to “AC Motors”

### Who is online

Users browsing this forum: No registered users and 2 guests