Your question is difficult to answer in a simple way.

There are many means to regulate the conveyor motor's speed to a setpoint such as inverters, fluid clutches, DC solid-state rectifier regulators

There are a number of factors that induce error:

1. motor design such as electrical slip <1-3% depending or rotor design; AC-asynchronous, AC-synchronous, DC

2. AC-asynchronous ( most common electrical motor design) motor size - motor slip can be controlled to a tighter and lower electrical slip with a higher design load: 2% for small motors and down to < 0.8 % for large designs with an A NEMA equivalent slip rated eff.

3. instrumentation: speed loop error control - operating over the motors AC-asynchronous speed range would make maintaining to <1% of the selected speed significantly more difficult than to 1% of full speed.. So its impoortant to know if your speed setpoint will be fixed or variable. Other motor designs will require different control strategies.

Your question on a need for speed and position accuracy: one application is in the automotive chain drives on their assembly lines. A second application, but not conveyor related, might be a AC-generator which needs to run at the grid line frequency usually within +/- 1%. These are accomplished by AC-sychronous motors. But, then you get inot power-factor correction and lead-lag phase angle adjustments which distort the target setpoint.

If acceleration control is not an issue, then use a AC-sychronous motor that runs at a constant RPM regardless of demand load, unlike a AC-asynchronous motor where the motor speed varies with load. ■

When using an inverter at the low end of the motors speed range you may experience cogging or percetable speed changes that wil exceed 1% due to the step configuration of the rebuilt AC sine wave. Some inverters have a 6 step wave form others 12 step or others a pulse width modulated ( higher steps at the low speed range starting at 24 steps more or less).

As previoulsy stated, accuracy will depend on the conveyor speed range and target. ■

There is no allowable deviation in speed or in other words there is no speed range of a synchronous motor unless a cycloconverter (type of inverter) is applied to regulate speed.

THe synchronous motor will deliver to the accuracy of your lelectrical line frequency variation. ■

Usually, small packaging conveyors require exact speed, this is usually achieved using Servo motors. ■