Can I acquire motor shaft position using my motor and VFD?

The project I am working on is to design the control system for a shock dynamometer. The shock dyno will look a little something like this;


So one of the main objectives in my project is to produce a plot as seen below;


The force will be data coming from a load cell.

The Displacement will be the linear displacement of the shock being tested (the compression/rebound). To clarify what I mean, I have included the figure below;


My question is: Do you think I would be able to acquire the shaft position from my motor using my VFD?

I called AutomationDirect (the manufacturer of the VFD) and asked them this question and they told me no considering the motor I am using (3 phase) is not a servo motor but I just wanted to double check with the forums to make sure. I tried reading the encoder feedback registers through Modbus and moving the shaft by hand to see if any values changed but no luck. I'm guessing I may have to implement some kind of proximity sensor in order to acquire the data for displacement. Due to the design of the dyno, I don't think I would be able to attach an external rotary encoder to the shaft of the motor. Any suggestions?

In case it helps, below is a picture of the nameplate on the motor and also the link and model of the VFD I am using.


VFD: DURApulse GS3-21P0 AC Drive
VFD Manual: https://cdn.automationdirect.com/static/manuals/gs3m/gs3m.pdf

Thank you.

-Kevin

1750 RPM = 30 RPS hence one shaft rotation takes approximately 33 ms.

The VFD itself will not be able to inform you about every 90 Deg. of shaft rotation; an encoder attached to the motor shaft will do it, however, you will need a specialized device to acquire the encoder signals, a High Speed Counter.

I think a motor shaft flag and four proximity switches(0 Deg, 90 Deg, 180 Deg and 240 Deg) will also do and it will be more cost effective

At nominal speed the motor shaft will take 8.25 ms to rotate 90 Deg; the Input Module the proximity switches will be connected to should be able to detect a 8ms change of state (including the Off/On and On/Off lag); most of the major platforms' Digital Input Modules provide said requirements and some PLC one-board Inputs will be able to provide it too.

If you need to go above nominal motor speed, a High Speed Digital Input module will give you enough cushion to process the proximity switches signals.

You need an encoder. Either a rotary at your output shaft, or a linear at the rail. Linear is best. They are quite reasonable these days.

keithkyll said:

You need an encoder. Either a rotary at your output shaft, or a linear at the rail. Linear is best. They are quite reasonable these days.

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+1 to this. Keyence makes some really good laser distance meters.

http://www.keyence.com/products/sensor/laser/index.jsp