Can I control asynchronous motor accuracy as servo

I have worked a great deal designing PM synchronous servo motors and their systems. Generally I work with precisions of 20 micron or less, this application is only about 800 micron of positioning accuracy. Following are some of the principles that I use to guide me through applications that might help you.

First- Accuracy is a function of the system not just the motor. The motor is merely a device for converting current into torque or force. Your system is comprised of the following: The Load, this is the mechanical portion of the system including the work and cutters; stiffer is always better when it comes to precision and if your load is too flexible the required precision could be impossible. The Controller/Amplifier this is where the servo loop is closed, system tuning parameters are set and the current is regulated to the motor windings, it is best to speak with a manufacture representative to ensure that you have to correct control for you application as this can be a complex subject. The Encoder or feed-back device, higher resolution is always better; I find I need a minimum of 10x resolution to my desired system accuracy. Finally the Motor, in positioning application I generally find lower inertia is better for accuracy, but in velocity control (which sounds more like what you need) I find higher inertia to be better for accuracy; this is because velocity control applications tend not to need high accelerations or rapid changes in speed, this means high inertia is your friend, it tends to smooth things out and help maintain a constant speed.

The technology Synchronous vs Asynchronous: Synchronous tend to be lower cost up to 1.5 kw, have lower inertia and higher acceleration rates for better positioning control. Asynchronous tends to be more cost effective above 2.0 kw and has higher inertia and less of an ability to change speed rapidly.

If I understand the application correctly you are looking for a continuous smooth speed which is more suited to the asynchronous motor. Your encoder resolution of 1024 ppr seems very low, you should probably look into improving that, 20,000 ppr encoders have become very common and cost effective in recent years. Also look closely at the controller and ensure it is adequate for the application and motor. Keep in mind you may need to improve more than one of the components I stated above.