Ultra-precision Machine Tool Contact Detection via Optical Scanning
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Solution Overview
Problem
Existing machine tools with frictionless movable axes supported by fluid bearings face challenges in accurately determining the machining start position due to the difficulty in detecting workpiece position and the risk of tool or workpiece movement from the contact position, especially when slight forces are applied, leading to inaccuracies in nano-unit machining.
Innovation Solution
A machine tool equipped with position detectors, contact point detecting means, and retreating means that utilize fluid bearings to accurately detect the machining start position by scanning the workpiece surface and setting the tool position based on position deviations, allowing for precise contact detection and automatic storage of machining start coordinates, with servo gains set to detect contact with minimal force exertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque-over detection method is used to detect workpiece position, then workpiece position can be detected, but the torque acts on the tool and workpiece causing them to move from contact position, making it difficult to determine position with nano-unit accuracy
Solution Approach 1:
The patent replaces the mechanical torque-over detection method with a non-contact optical measurement system using a microscope and image processing. This substitution eliminates the mechanical force application that causes position displacement, allowing workpiece position detection without affecting the contact position accuracy. The optical system captures images of the workpiece surface and calculates positions based on image coordinates, completely avoiding the torque-induced movement problem.
2Reliability
If limiting output torque of actuator is used to move tool toward workpiece, then tool can be advanced safely, but position deviation exceeds skip deviation amount making it difficult to determine contact position with nano-unit accuracy
Solution Approach 1:
The patent performs preliminary positioning of the tool near the workpiece using the actuator with limited torque, then uses optical measurement to precisely determine the contact position without requiring the actuator to achieve the exact contact point. The tool is preliminarily positioned close to the workpiece surface, and the precise contact position is then determined through image processing of the workpiece features, separating the rough positioning function from the precise measurement function.
3Manufacturing precision
If microscope is used to measure distance between blade tip and workpiece, then tool can be brought very close to workpiece, but limited focal depth causes blade tip to no longer be seen as machining progresses
Solution Approach 1:
The patent transitions from one-dimensional depth measurement (blade tip to workpiece surface distance) to two-dimensional surface coordinate measurement. Instead of measuring the Z-axis distance which is limited by focal depth, the system measures X-Y coordinates of workpiece features on the surface using the microscope's image plane. This dimensional shift allows measurement of workpiece positions across a larger area without being constrained by the limited focal depth of the microscope.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate detection and setting of the machining start position with high precision, reducing the risk of tool or workpiece movement and ensuring nano-unit accuracy in ultra-precision machining by using fluid bearings to detect position deviations and adjust the tool position accordingly.
Implementation Method 1
a machine tool which machines a surface of a workpiece by moving a tool relative to the workpiece from a start point of machining using movable axes supported by fluid bearings
Implementation Method 2
the position detectors for detecting positions of the linear axes may comprise linear scales having detection resolution of 10 nm or less
Data Source
AI summary
An ultra-precision machine tool capable of accurately detecting a machining start position, in which movable axes are supported by fluid bearings. A workpiece is mounted on a rotary table of a B axis, and the rotary table is mounted on an X axis that is a linear motion axis. A tool is mounted on a Y axis. The Y axis is mounted on a Z axis. The X axis is moved reciprocally each time the Z axis is moved a predetermined amount, a machining surface of the workpiece is scanned, and it is determined whether or not position deviation of the X, Y and B axes reaches or exceeds a reference value. The Y axis is driven and the tool is moved toward the workpiece a predetermined amount, and the above-described scan is performed. When the position deviation of the X, Y and B axes reaches or exceeds the reference value it is determined that contact between the tool and the workpiece has occurred, and this contact point is stored as the machining start position, the Y axis is skipped, and the tool is moved a predetermined amount in a direction away from the workpiece, thus enabling a point of maximum protrusion from the machining surface of the workpiece to be simply detected as the machining start point.