Position Measuring Devices in CNC Machines
The accuracy of positioning in CNC machining tools is achieved by measuring the position or displacement of the slide and comparing with the commanded position in part program. The servo system actuates the slide such that the error which is the difference between programmed position and command position is brought to zero. The position of the slide can be measured directly by fitting a linear transducer to the slide is called direct measuring and indirectly by mounting a rotary transducer to the ball screw of the slide or mounting the transducer on the servomotor shaft is called indirect measurement.
Direct measurement is preferred for more accurate positioning, now a days majority of CNC machines are designed with the feed back devices mounted on the rear side of the servomotor any backlash in ball screw can be compensated in software.
Position measuring devices can be generally classified as:
Direct measuring Devices.
Indirect Measuring devices.