In a CNC machine tool, the function of an interpolator is to generate

The correct option is: "reference signal prescribing the shape of the part to be machined "

An interpolator in a CNC (Computer Numerical Control) machine tool is a vital software or hardware component that coordinates the movement of multiple axes (such as X, Y, and Z) to produce a desired path or contour.

To understand why this option is correct, let's break down the role of the interpolator step-by-step:
1. Path Generation: The part program provides coordinates of discrete points (e.g., start and end points of a line or circle). However, the machine tool must move continuously along a precise geometric path between these points to form the required shape.
2. Generation of Reference Signals: The interpolator calculates intermediate coordinate points along the programmed path at a high speed. It then converts these coordinates into a series of reference velocity/position command signals (often electrical pulses or digital values) for each axis servo drive system.
3. Prescribing the Part Shape: By continuously outputting these coordinated reference signals to the axis controllers, the interpolator ensures that the cutting tool traces the exact profile (linear, circular, or parabolic) required to machine the physical shape of the part.

Let us briefly analyze why the other options are incorrect:
• Signal for the lubrication pump: This is a simple auxiliary command (M-code) handled by the Programmable Logic Controller (PLC), not the interpolator.
• Error signal for tool radius compensation: Tool radius compensation calculations modify the coordinates of the path before interpolation, whereas error signals themselves are typically generated by feed-back loops (comparators) in the servo drive system during execution.
• NC code from the part drawing during post processing: This task is performed by Computer-Aided Manufacturing (CAM) software during the pre-machining phase, whereas the interpolator operates in real-time inside the CNC controller during the actual machining process.