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Unformatted text preview: NC-3e-S 11-14, 14/06, 06/04/07Chapter 7NUMERICAL CONTROLREVIEW QUESTIONS7.1What is numerical control? Answer: As defined in the text, numerical control (NC) is a form of programmable automation in which the mechanical actions of a machine tool or other equipment are controlled by a program containing coded alphanumeric data.7.2What are the three basic components of an NC system?Answer: The three components are (1) the part program of instructions, (2) the machine control unit, and (3) the processing equipment (e.g., machine tool) that accomplishes the operation.7.3What is the right-hand rule in NC and where is it used?Answer: The right-hand rule is used to distinguish positive and negative directions for the rotational axes in NC. Using the right hand with the thumb pointing in the positive linear axis direction (+x, +y, or +z), the fingers of the hand are curled in the positive rotational direction for the a, b, and caxes.7.4What is the difference between point-to-point and continuous path control in a motion control system?Answer: Point-to-point systems move the worktable to a programmed location without regard for the path taken to get to that location. By contrast, continuous path systems are capable of continuous simultaneous control of two or more axes, thus providing control of the tool trajectory relative to the workpart. 7.5What is linear interpolation, and why is it important in NC?Answer: Linear interpolation is the capability to machine along a straight-line trajectory that may not be parallel to one of the worktable axes. It is important in NC because many workpiece geometries require cuts to be made along straight lines to form straight edges and flat surfaces, and the angles of the lines are not be parallel to one of the axes in the coordinate system.7.6What is the difference between absolute positioning and incremental positioning?Answer: In absolute positioning, the workhead locations are always defined with respect to the origin of the NC axis system. In incremental positioning, the next workhead position is defined relative to the present location.7.7How is computer numerical control (CNC) distinguished from conventional NC?Answer: CNC is an NC system whose machine control unit is a dedicated microcomputer rather than a hard-wired controller, as in conventional NC.7.8Name five of the ten features and capabilities of a modern CNC machine control unit listed in the text.Answer: The ten features and capabilities identified in the text are (1) storage of more than one part program, (2) various forms of program input, such as punched tape, magnetic tape, floppy diskette, RS-232 communications with external computers, and manual data input, (3) program editing at the machine tool, (4) fixed cycles and programming subroutines (macros), (5) linear and circular interpolation, (6) workpiece positioning features for setup, (7) cutter length and size compensation, (8) acceleration and deceleration calculations when the cutter path changes abruptly, (9) communications interface, and (10) diagnostics to...
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