Rotational Speed Estimation for Machine Tool Spindles
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Solution Overview
Problem
Current methods for measuring the rotational speed of tools on rotating spindles in machine tools are either time-consuming due to redundancy or invasive, as they require additional sensors, leading to potential acquisition errors in image acquisition for geometrical feature measurement.
Innovation Solution
A method that estimates rotational speed by determining a preselected interval of speed values, calculating image acquisition periods, and using a similarity rule to identify the most similar image couples, allowing for precise speed determination without additional hardware, thus enabling accurate image acquisition at desired angular positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a speed or position sensor is arranged on the spindle to obtain real-time speed data, then measurement precision of rotational speed is improved, but device complexity and invasiveness increase
Solution Approach 1:
The patent creates a virtual copy of the speed sensor functionality by using the existing image acquisition system to capture tool position information. Instead of adding a physical speed sensor, the system processes images to infer rotational speed, effectively copying the measurement function through software processing of visual data already captured by the vision system.
Solution Approach 2:
The patent replaces the mechanical speed sensor system with an optical-computational system. The physical speed or position sensor on the spindle is substituted by using the image acquisition device to capture tool shadows and processing these images computationally to determine rotational speed, thereby eliminating the need for additional mechanical sensing components.
2Measurement precision
If a large number of redundant acquisitions are performed to determine rotational speed, then measurement precision is improved, but productivity decreases due to increased execution time
Solution Approach 1:
The patent applies partial action by using a limited number of image acquisitions (just enough to establish the relationship between acquisition period and tool position) rather than performing a large number of redundant measurements. The method determines rotational speed from the temporal relationship between a small set of acquisitions, avoiding the need for excessive redundant data collection while maintaining sufficient measurement precision.
Solution Approach 2:
The patent implements feedback by using the determined rotational speed information to adjust and optimize subsequent image acquisition timing. The system acquires images at temporal cadences calculated based on the estimated rotational speed, creating a feedback loop where speed measurement informs acquisition strategy, thereby improving both precision and efficiency without requiring redundant acquisitions.
3Productivity
If images are acquired at a temporal cadence based on nominal rotational speed, then productivity is improved by reducing acquisition time, but measurement precision deteriorates due to speed deviations from nominal values
Solution Approach 1:
The patent applies preliminary action by first determining the actual rotational speed of the tool before proceeding with the main measurement acquisitions. The system performs an initial speed estimation phase to establish the true rotational characteristics, then uses this information to calculate appropriate acquisition periods. This preliminary speed determination ensures that subsequent high-speed acquisitions are timed correctly, maintaining both productivity and precision.
Solution Approach 2:
The patent implements dynamics by making the image acquisition temporal cadence adaptive rather than fixed. The system dynamically adjusts the acquisition period based on the actually measured rotational speed rather than relying on nominal speed values. This dynamic adjustment allows the system to optimize acquisition timing in real-time, maintaining measurement precision while maximizing productivity across varying operational conditions.
Data Source
AI summary
In a machine tool (1) comprising a rotating spindle (2) and a vision system (7) for acquiring images of a tool (3) mounted on the spindle, for each value (VC) of an interval (ICN) of preselected rotational speed values centered on a nominal rotational speed value (VN) of the spindle, an image acquisition period (TA) is determined, that is a multiple of the rotational period (TR) of the spindle calculated for that preselected speed value and compatible with the vision system, and, while the spindle is rotating at the nominal rotational speed, a representative couple of tool images that are temporally spaced apart from one another of the image acquisition period is obtained, in order to obtain an estimated speed value (VS), associated to the nominal speed value, by selecting that preselected speed value to which the representative couple of images that are the most similar to each other on the basis of a similarity rule corresponds.