Choosing a PLC and an optical encoder for a high-precision rotary table

We consider making a rotary table capable of two operation modes: 1) rotating at speeds up to 3 rpm, and 2) positioning with precision of 60 arcseconds. This gives us 21600 positions per turn and 1080 positions per second at max speed. Current position must be recorded upon signal from an ultrasonic scanner (which is a blackbox atm) with aforementioned precision level to be fetched by a PC later.

This kind of control is new to our company. I think it could be implemented using a PLC with high-speed inputs and an incremental optical encoder attached to a VFD motor shaft. Am I right? Particular products? Any suggestions at all?

Thank you!

Positioning, precision... I think you need a servo sollution...

Jack

Yegor said:

21600 positions per turn and 1080 positions per second at max speed.

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Now how about?
Yes you could use a VSD but why would you - Much harder to implement and you must design your own controller - and create your own code
also high speed digital inputs are usually not good enough think about a high speed counter card (also called incremental encoder inputs)

+1 Servo
Plus they have high speed capture current position inputs

Now how about?
the precision of the mechanics?
Gear Box Precision?
The ultrasonic "Black Box" - how fast is it?
response time comes into it (rise time of the sensor and digital input)?
PLC Scan time to determine when Digital input changed?

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I had exactly the same doubts but was too shy to say that. Our department doesn't even specialize in motion control but we were tasked to consider such system anyway. No gear or ultrasonics info provided. And the client seems unaware of any data transmission latencies in their ridiculous requirements. I'm gonna tell my boss that the task looks like an April Fool's Day joke at the moment. Thank you for assuring me.

There are gearboxes for servo motors with a precision of 5-15 arcseconds.
Dont know about standard gears, but I doubt that a standard gear will be OK for that precision.
How much Torque do you need ?

use an encoder card for example a WAGO PLC.
this card will also drive a servo, or any other kind of motor.
it will stop on exact count.

You're looking at using a servo motor with probably a Harmonic drive gearhead. I wouldn't bother trying to use a VFD - they're not good for any precision positioning unless it's a special case.