Numerical Controller Tool Tip Point Control Backlash Reduction

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Solution Overview

Problem

Conventional numerical controllers for five-axis machining experience backlash during tool tip point control, leading to compromised machined surface quality due to excessive compensation functions.

Innovation Solution

A numerical controller with a control point interpolation unit that generates movement instructions for a third movement path by linearly interpolating the second movement path, determining if the distance between paths is within a predetermined tolerance, and outputting instructions to minimize backlash by maintaining the path deviation within an allowable range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If tool tip point control is implemented with curved control point path, then tool tip point moves on instructed movement path, but control point path reverts causing backlash

Engineering Contradiction:

Improvetool tip point position accuracyVSAvoidcontrol point path stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The control point path is segmented into multiple linear blocks instead of being a continuous curved path. By dividing the curved path into discrete linear segments, the system maintains tool tip point accuracy while preventing path reversal within each block, thereby eliminating backlash.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of generating a curved control point path and then linearizing it, the invention inverts the approach by directly generating linear control point paths that collectively approximate the desired curved tool tip point trajectory. This inversion prevents path reversal from occurring in the first place.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If backlash compensation function is activated, then control point path reversal is corrected, but machined surface quality deteriorates

Engineering Contradiction:

Improvecontrol point path stabilityVSAvoidmachined surface quality

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention extracts and removes the need for backlash compensation functions by fundamentally changing the control point path generation method. By using linear interpolation to create straight-line control blocks, the source of backlash (curved path reversal) is eliminated, making compensation functions unnecessary and thus preventing their negative impact on surface quality.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If control point path is linearly interpolated, then backlash is suppressed, but tool tip point path deviation increases

Engineering Contradiction:

Improvecontrol point path stabilityVSAvoidtool tip point position accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The invention changes the interpolation parameters by adjusting the number and length of linear blocks to optimize the balance between path stability and tip point accuracy. By carefully selecting interpolation parameters, the system achieves backlash-free operation while keeping tool tip point deviation within acceptable tolerances.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10073432B2Numerical controller having tool tip point control function

Publication Date: 2018.09.11 FANUC LTD

AI summary

In a numerical controller having a tool tip point control function, a provisional tool tip point movement path calculation unit calculates a fourth movement path of a tip point of a tool on the basis of a third movement path obtained by linearly interpolating a second movement path for moving a control point of the tool along the second movement path, and a post-linear interpolation movement instruction output unit outputs a third movement instruction if it is determined that the difference between a first movement path for moving the tip point of the tool along the first movement path and the fourth movement path is within a predetermined tolerance.