Depending on the required precision, you can use one of the built-in analog inputs, or a higher precision and more capable analog input add-on module.  That covers the generic 0-10V, +/-10V, 0-20mA, 4-20mA types of inputs.

For angle sensing, there are many types available.  Given the nature of the system, you probably want an angle sensor intended for industrial applications (electronically noisy environments), which generally comes down to 4-20mA or 0-20mA outputs.  Then you need a way to calibrate the input signal, or convert it to a 0-100% type of signal and put a PID on the movement control to peak the output while monitoring the angle.  At various times throughout the day, you can capture values and map out optimal values once the peak output has been obtained, save to a table, and use it as the starting point for tomorrow's movements to get optimal angle.

 You might find this tool useful

ABIR2997

Or maybe can you give some 2 or 3 types of these sensors please :)