Designing Test Bench for Torque and RPM Testing

[werkit217]

I am currently designing a test bench for our in-house manufactured air motors. After consulting with the line leader, this specific motor have a operating torque at 38-42 but was not able to provide me with units, running at 1300 rpm. I am in the process of verifying if the units of torque are in foot pounds as suggested by the line worker.

After spending quite sometime reading literature online for testing torque, rpm, and back travel, I have yet to find a suitable reference. This is where asking for your opinions and guidelines to make sure I acquire all the necessary components to test the air motors.

I have already designed a fixture, and in the process of pricing out the appropriate shaft (disc) coupling, a torque transducer, and a transducer read-out analyzer. We will hook the motors up to an airline to run them.

What would be a reasonable way to cut the air supply to the motors then apply a magnetic brake to stop the motor? How exactly to magnetic brakes work?

I also need a way to test the back travel the motors, I have never tested them for them so need some help to come up with a way to test that.

The existing testing method of these motors is quite unacceptable. They hook up the motors to an airline at 76 psi, and are ran in for about 20 minutes, no way of testing them nor fixture in place to hold the motor.

We are planning on hooking up

 

[RyanPatrick]

Werkit,

I work in a manufacturing plant where we produce hydraulic pumps. We use air motors to power some of the pumps we produce.

First of all, I highly recommend you design a fixture that sits flush with the top of a bench that allows you to drop the air motor into it and secure in place to counter the torque seen during operation. The rest of the fixture sits under the bench so 1) it is away from the operator and 2) it saves space. It sounds like you might be in the process of doing this already.

Cutting the air supply: on one test stand in our plant we use a very simple air shut-off valve that is right on the air supply line. Works well and is very cheap. On another test stand we use a valve (VAS-42 or VA-42 in house). The beauty of the valve is that you can also integrate it into your test stand so that when you shut-off the valve you can write a PLC program that might let you start taking measurements exactly after the air has been cut. Don't know if you need this capability or not, but thought I'd let you know it's an option.

One way to measure your rotational velocity is to use a rotary encoder. These are nice if you have the money. Set up is fairly easy and a simple LabView application will allow you to read and record the output (if your ISO compliant the recording capability is great to have). The rotary encoder can be incorporated right into your fixture under the bench. Another way, and forgive me but I completely forgot the name of the device, is to measure the vibrational frequency of the air motor. The device has an array of basically tuning forks that have an individual resonant frequency. Whatever frequency your motor is running, the associated fork will vibrate rapidly with respect to the others. This is much cheaper, however record keeping is more primitive and time consuming. Also, you have a separate tool just sitting on your bench.

Magnetic brakes (I think there are multiple definitions of this) but, a great implementation of them is to basically build a DC motor. Someone with a lot more experience with DC motors should explain how to set this up, but you basically have your windings and magnets. As the shaft spins you can flip a current on through the windings that creates a counter torque on the shaft to slow it down. The amplitude of the current determines the torque applied to the shaft (too great a torque can wear down your components, too small a torque doesn't stop the motor very fast and wastes takt time). Again, before you look into doing this, please consult an expert on this as I just wanted to put in little bit.

Bottom line from me, your fixture would be best designed into the bench and have all the components sitting under the bench. Use locating pins with some sort of top down clamping device to lock the motor in place and this way you can incorporate all of your components in line sort of stacked on top of each other so each one comes in contact with the drive shaft (in the top mount of your fixture you couple the drive shaft of the air motor to a separate shaft that is permanently in the fixture). If you have the resources to go with the more expensive stuff and set up a PLC/LabView application, by all means do so as it will pay off in time saved and ease of use in the end. If you crunch the numbers and use your plant's overhead cost I believe you will be able to justify this as well.

Hope it all comes together!