Inductive Tool Integrity Checking for Short-Duration Contact Detection
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Solution Overview
Problem
Existing systems for checking the integrity of rotating tools in machine tools face challenges in detecting intermittent and short-duration contacts between the tool and workpiece, especially with small tools, due to high rotation speeds and dynamic behavior of bearings, leading to unreliable detection and electrical connectivity issues.
Innovation Solution
A detection circuit with a half-bridge configuration using AC excitation voltages 90° out of phase and an RMS converter, along with a microprocessor for real-time signal processing, allows for reliable detection of short and intermittent contacts through a high crest factor signal and low average time constant, and a sliding contact mechanism for stable electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional inductive detection systems are used to detect tool-workpiece contact, then the system structure is simple, but the detection reliability is poor for intermittent and short-duration contacts
Solution Approach 1:
The patent implements dynamic signal processing with adjustable filtering parameters that adapt to different contact durations. The system uses variable time constants in the integration circuit and programmable detection thresholds that can be adjusted based on the specific machining operation and tool rotation speed, enabling reliable detection of both brief intermittent contacts and sustained contact conditions.
Solution Approach 2:
The patent introduces an intermediary signal processing stage between the inductive sensor and the control system. This intermediary circuit includes operational amplifiers, integrators, and programmable logic that condition the raw detection signal, filter noise, and generate standardized output signals that reliably indicate contact conditions to the control system.
2Productivity
If the tool rotation speed is increased to improve productivity, then the production output increases, but the contact detection becomes more difficult due to shorter contact duration
Solution Approach 1:
The system dynamically adjusts its detection parameters based on the measured or pre-set tool rotation speed. When high rotation speeds are used, the system automatically reduces integration time constants and adjusts threshold levels to capture the shorter duration contact signals that result from faster tool rotation, maintaining detection capability across the full range of operational speeds.
Solution Approach 2:
The patent employs periodic sampling of the detection signal at frequencies synchronized with or higher than the tool rotation frequency. This periodic measurement approach ensures that even brief contact events occurring at any phase of the rotation cycle are captured, enabling reliable detection regardless of the tool's rotational speed.
3Manufacturing precision
If small diameter tools are used to achieve precise machining, then the machining precision improves, but the tool is more susceptible to breakage and harder to detect
Solution Approach 1:
The system changes its detection parameters specifically for small diameter tools, using higher sensitivity settings, lower threshold values, and adjusted integration times that are optimized for the weaker inductive signals produced by smaller tool masses. The control unit can be programmed with tool-specific parameters that automatically adjust the detection system's sensitivity based on the installed tool's diameter and material properties.
4Duration of action of stationary object
If non-conductive bearings are used to reduce friction and wear, then the bearing life and efficiency improve, but the electrical connectivity for detection purposes deteriorates
Solution Approach 1:
The patent introduces an intermediary electrical connection system that bridges the gap created by non-conductive bearings. This may include conductive elements integrated into the bearing housing, inductive coupling mechanisms, or capacitive sensing arrangements that transfer the rotational position and contact information from the tool holder through the non-conductive bearing assembly to the detection circuit without requiring direct electrical contact through the bearings themselves.
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
The system provides reliable and real-time detection of tool integrity, even with small and rapidly vanishing contacts, and can be applied to tools with limited access and non-conductive bearings, ensuring accurate and timely tool replacement.
Implementation Method 1
An inductor (4) comprising a winding wound on a portion of an annular core made of ferromagnetic material... detect variations caused in these circuit elements by the contact between the metal tool and the - also metallic - processed workpiece
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A checking system (3) connected to a tool holder - for example a rotating shaft (5) - on a machine tool for checking the integrity of a tool while machining a metal workpiece (2) includes a detection circuit (18) including an inductor (4; 64) with an annular core (7) arranged near the tool holder and windings (9) wound on the annular core. On contact between the tool and the metal workpiece, a circuit (C; C ') which includes part of a support structure (1) of the machine tool and which crosses the inductor closes, causing variations in the electrical parameters of the detection circuit that allow to detect the contact. The detection circuit has a half-bridge configuration with two resistive branches powered by alternating excitation voltages substantially 90° out of phase with respect to each other and comprising respectively the inductor and a reference resistor (25), and a detection branch for generating and transmitting the detection signal to a control unit (10). In a preferred form, the reference resistor has a resistance substantially equal to the impedance of the inductor.