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Dynamic Load Cell controlling force applied by a Servo
Kiranashah
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11-02-2015 04:47 AM
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I am trying to build a Dynamic Scratch Testing rig, however I am unsure what components would best suit my needs. Looking through the NI catalogue they offer a range of products that may fit my application but with limited knowledge on them I was hoping some of you could point me in the right direction.
I'm looking for a linear servo that I can control with a load cell to apply a dynamic force from a vertical position onto a test specimen which will be moving in a horizontal axis.
The load cell and vertical servo will be operating in a range of 0-100N with a travel distance of around 50mm, and the horizontal servo will travel a maximum distance of 25mm at a set speed
I need to be able to control a set rate of force applied in relation to the horizontal speed. e.g. Applying a force from 1-20N over a 10mm horizontal distance over 60 seconds.
Could anyone suggest the type of Load Cell, Servos and Controller I would be looking for to complete this task?
antsundq
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11-06-2015 03:07 AM - edited 11-06-2015 03:07 AM
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Hi,
This is a rather specific question and I think it might be a good idea to contact a sales representative directly. I will however try to help you the best I can.
To start you will need to determine how much torque you need the motors to produce. The torque M is related to the force F as Fr=M where r is the length of the lever arm or displacement from the axis. The speed v which which you can move the probe will be related to r as v=2*PI*f*r where f is the number of rotations per minute. What you will need to ensure is that the torque is enough for every motor speed to ensure that f*M > Fv/(2PI). Note however that the torque is in general a function of the motorspeed f, so you will have to look at the specifications and make sure that you are within bounds for each point in the motion profile. What remains is to choose a proper gearing.
What kind of controller are you planning to use? The cRIO system together with the NI SoftMotion package offers a very robust system that allows you to control the trajectory the motor moves and this you will be able to control through the software. There are basically two ways of controlling the motor. You can either use a drive module, such as the NI 9502 or NI 9505, or you can use a drive interface module such as the NI 9514 together with an external drive.
The force applied can be set using the software, through setting a specific torque. If you want you can implement an external sensor to verify the applied force.
/Anton
