Forces required to accelerate a mass on a spring

[JohnDear]

Hi,

I am currently working on a project and have become stuck on what should be a relatively simple problem (I thought).

Basically I am using a DC motor to provide a force on a crank that compresses a piece of rubber.

The movement includes some acceleration.

I am trying to use the motor current to find out the motor torque (use torque constant), and then force profile of the piece of rubber.

What i have done is perform the movement without the rubber, data log the motor torque.

Then perform the movement with the rubber, data logging the new motor torques.

Without thinking too much about it, I then subtracted the free motor torque from the motor torque with rubber, and said the result was 'torque due to compressing the rubber'. Calculated force from that, and results seem ok.

My question is:

Does acceleration effect the results when using my method? If so how? And how could i minimise this under circumstances where acceleration must be high?

Also if anyone has some information on this type of procedure I'm using, (papers etc) that would be great.

thanks,
John

 

[JohnDear]

After thinking about it I think my approach is fair.

In the free motion case F = ma.

In the rubber compression case F = ma + k.d (k the spring constant of rubber assuming it behaves linearily).

I see no reason why I can't treat the two force components independently.

Only issue I can see is the effect of loading on friction (not accounted for in my model, but inherent in both my measurements), I think this may increase with loading, but can assume the increase to be insignificant.

Anyone with greater insight than me into this type of problem would love to hear from you,

thanks,
John

 

[astrokreng]

Dear John,

Thank you for sharing your project with me. From your description, it seems like you are trying to determine the forces required to compress a piece of rubber using a DC motor. This is certainly an interesting problem and I would be happy to provide some insight.

First, let's talk about the forces involved in this process. When the motor applies a torque on the crank, it causes the rubber to compress. This compression creates a restoring force, which is proportional to the displacement of the rubber. This restoring force is what determines the acceleration of the mass on the spring. In other words, the greater the force applied by the motor, the greater the acceleration of the mass.

Now, to answer your question about whether acceleration affects the results, the answer is yes. When the rubber is compressed, it also stores potential energy. This potential energy is then converted into kinetic energy as the rubber expands back to its original shape. This expansion results in an acceleration of the mass, which means that the force required to compress the rubber is not constant throughout the entire movement. Therefore, your method of subtracting the free motor torque from the torque with rubber may not accurately represent the true force profile.

To minimize the effect of acceleration on your results, you can try to reduce the acceleration of the mass by using a slower motor speed or a lighter mass. Additionally, you can also try to measure the force directly using a force sensor, rather than calculating it from motor torque. This will give you a more accurate representation of the force profile.

As for information on this type of procedure, you may find some relevant papers by searching for "force measurement in spring systems" or "force profile of compressed rubber" in scientific databases such as Google Scholar or ScienceDirect.

I hope this helps and good luck with your project!