Question

Q1) Identify and briefly describe the three basic components of a numerical control system. Q2) what is the difference between point-to-points and continues path in a motion control system? 03) what is the deference between absolute positioning (coordinate) and incremental positioning? Q4) what is the difference between an open loop positioning system and closed a closed loop positioning system? Q5) Under what circumstances is a closed loop positioning system preferable to an open loop system?

Answer 1

Ans. 1) Three basic components of a numerical control system :

1. Program of instructions.
2. Controller unit, also called machine tool unit.
3. Machine tool or other controlled process.

The program of instructions is the detailed step by step set of instructions/commands that direct the actions of the processing equipment.

Controller unit consists of microcomputer and related control hardware that stores the program of instructions and executes it to mechanical actions of the machine tool.

Machine tool performs useful work and accomplishes the processing steps to transform the starting workpiece into a completed part. Its operation is directed by the MCU.

Ans. 2) Point-to-point systems Vs Continuous path system

In point-to-point systems, tool moves on the worktable to a programmed location without regard for the path taken to get to that location. Once the tool moved, processing action is accomplished by the workhead at the location, e.g. drilling a hole.

In continuous path systems case, the tool performs the process while the worktable is moving, thus enabling the system to generate angular surfaces, 2D/ 3D contours in the workpart. E.g. milling operations.

Ans. 3) Absolute Vs Incremental Positioning:

In absolute positioning, the workhead locations are always defined with respect to the origin of the axis system.

In incremental positioning, the next workhead position is defined relative to the previous location of the tool.

Ans. 4)   Open-loop Vs Closed-loop Positioning Systems

An open-loop positioning system takes input under the consideration and doesn’t react on the feedback to obtain the output. There are no disturbances or variations in this system and works on fix conditions.

A closed loop positioning system record the output instead of input and modify it according to the need. It generates preferred condition of the output as compared to the original one.

Ans. 5)

A closed loop positioning system preferred, where, more accurate complex surface required on work and also work is affected by noise.