Machine Tool Spindle Load Monitoring for Early Abnormality Detection
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Solution Overview
Problem
Existing main spindle monitoring systems in machine tools fail to detect abnormalities, such as preload loss and foreign matter entrapment, during cutting operations due to reliance on thresholds set for machining influences, leading to late detection of serious conditions.
Innovation Solution
A main spindle monitoring device and method that includes a main spindle operation monitoring unit and a feed axis operation monitoring unit, which detect changes in load conditions during constant rotation speed and driving states to determine spindle abnormalities, using absolute value change amounts and variation width thresholds to differentiate between spindle and feed axis condition changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threshold-based monitoring system is used to detect main spindle abnormalities, then the system can identify serious conditions, but the detection occurs too late and abnormality detection precision deteriorates
Solution Approach 1:
The monitoring system is segmented into two independent monitoring units: one for main spindle operation (monitoring main spindle load) and one for feed axis operation (monitoring feed axis load). This segmentation allows each unit to focus on specific parameters, enabling early detection of main spindle abnormalities by comparing main spindle load changes independently of feed axis variations.
Solution Approach 2:
The feed axis operation monitoring unit serves as an intermediary reference. By monitoring feed axis load changes and comparing them with main spindle load changes, the system can distinguish between load variations caused by feed axis operations and those caused by main spindle abnormalities, enabling more precise abnormality detection.
2Reliability
If the monitoring threshold is set to account for machining influences, then the system avoids false alarms, but the threshold becomes too large to detect early stage abnormalities
Solution Approach 1:
The system extracts and separately monitors feed axis load changes from the overall system load. By taking out the feed axis operation effects and comparing them with main spindle load changes, the system can set lower, more sensitive thresholds for main spindle abnormality detection without being influenced by feed axis variations that would otherwise require higher thresholds.
3Measurement precision
If monitoring is performed only when cutting work is not being performed, then machining influences are avoided, but early stage abnormalities during cutting work cannot be detected
Solution Approach 1:
The monitoring system operates continuously during both cutting work and non-cutting operations. By continuously monitoring main spindle load and feed axis load and comparing their changes, the system maintains detection capability throughout all operational states, eliminating the time loss associated with waiting for non-cutting periods while avoiding false alarms through the comparative monitoring approach.
Data Source
AI summary
A main spindle monitoring device determines an abnormality of a main spindle in a machine tool. The main spindle monitoring device includes a main spindle operation monitoring unit and a feed axis operation monitoring unit. The main spindle operation monitoring unit monitors a change of an operation condition of the main spindle based on a main spindle load. The feed axis operation monitoring unit monitors a change of an operation condition of a feed axis based on a feed axis load. The abnormality of the main spindle is determined when the main spindle operation monitoring unit detects the change of the operation condition of the main spindle and the feed axis operation monitoring unit does not detect the change of the operation condition of the feed axis in a state where a constant rotation speed is commanded to the main spindle while the feed axis is driving.