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# Numerical Control System Interpolation Principle——Pulse Incremental Interpolation

Oct 14, 2019

Pulse incremental interpolation method, also known as stroke scalar interpolation method or reference pulse interpolation method, is the principle of analog hardware interpolation. The result of interpolation is to generate a single stroke increment and output to the servo system in a pulse mode. To drive machine component movements.

The interpolation procedure is relatively simple, but since the maximum speed of the output pulse depends on the time required to perform an operation, the feed rate is limited. This interpolation method is generally used in numerical control systems or open-loop numerical control systems where the feed rate is not very high.

Pulse incremental interpolation features:

• Only one unit stroke increment (1 pulse equivalent) is generated per interpolation.

• The fastest feed rate is closely related to the interpolation speed.

• The implementation method is simple, usually only by addition and shift operations, and easy to implement in hardware.

• Such interpolation algorithms include: point-by-point comparison method, minimum deviation method, digital integration method, target point tracking method, single-step tracking method, etc.

The point-by-point comparison method is a typical representative.

Point-by-point comparison interpolation

The point-by-point comparison interpolation method determines the coordinate feed direction of the tool by comparing the relative positions of the tool and the required interpolation curve point by point to machine the profile of the part.

The point-by-point comparison method approximates a straight line or an arc curve by a fold line, and the maximum error between it and a specified line or arc does not exceed one pulse equivalent, so as long as the pulse equivalent (the distance per step) is sufficient Small, you can meet the processing accuracy requirements.

For the point-by-point comparison interpolation calculation, the logical operation and arithmetic operation of the following four steps (also called four beats) are performed every step:

• Deviation Discrimination—Determines the deviation of the machining point from the specified curve to determine the direction of the X or Y coordinate of the feed.

• Give—Controls a coordinate feed with a pulse equivalent and moves closer to the specified curve to reduce the deviation.

• Deviation calculation—calculate the deviation of the new machining point from the specified curve as the basis for the next determination.

• End point judgment – judge whether it reaches the processing end point? If the end point is reached, the interpolation is stopped, otherwise it will return to the first step.

The above four steps repeat the above-mentioned cyclic process so that the desired curve trajectory can be completed.

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