تطبیق ​​تجزیه و تحلیل رگرسیون بردار پشتیبانی از دقت بازرسی حلقه بسته

This study investigates how closed-loop measurement error in CNC milling relates to two different inspection techniques. The on-line inspection of machining accuracy using a spindle probe has an inherent shortcoming because the same machine that produced the parts is used for inspection. In order to use the spindle probe measurement as a means of correcting deviations in machining, the magnitude of measurement errors needs to be quantified. The empirical verification was made by conducting three sets of cutting experiments at the state-of-the-art Cincinnati Arrow Vertical Machining Center. Three different material types and parameter settings were selected to simulate a diverse cutting condition. During the cutting, the cutting force and spindle vibration sensor signals were collected and a tool wear was recorded using a computer vision system. The bore tolerance was gauged by a spindle probe as well as a coordinate measuring machine. The difference between the two measurements was defined as a closed-loop measurement error and adaptive support vector regression analysis was used to predict these bore difference at various values of the explanatory variables. The results show the potential of improving production efficiency and part quality.

Discrete part manufacturing using computer numerical controlled (CNC) milling machines is common in modern manufacturing [1]. Depending on the accuracy and surface finish requirements, the machining parameters, which have a significant influence on part quality, need to be set properly [2] and [3]. Vibration in machining is particularly harmful in this regards [4], yet can be minimized through the use of computer simulation prior to the machining. The simulation can project the optimal range of cutting speeds and feed rates for a chatter-free machining, thereby producing less scrap and enhancing part quality. Since each machine tool exhibits disparate characteristics in stiffness, damping, and natural frequency [5], the importance of pre-machining simulation is applied to each machine, especially when the machine is newly acquired. Equally important in machining is the confidence in the measuring instruments from which part quality characteristics are ascertained. Part dimensional accuracy check has been largely based on the post-process inspection such as a coordinate measuring machine (CMM). CMMs are widely used in the manufacturing industry for precision inspection and quality control [6] and [7], and recognized as a reliable and flexible gauge suitable for assessing the acceptability of machined parts [8]. The downside of this technique is that non-conforming parts can be produced between inspections since there can be a significant delay between production and completion of inspection [3]. To remedy the problem, a machine mounted touch probe which has similar working principles as CMM [9] has started gaining popularity. The probe enables the measurement of machined parts while they are still fixed on the machine. By providing part size information directly into a CNC controller, a closed-loop process control can be realized in the form of real-time automatic tool offset to correct deviations or prevent defects in machining [10]. This is particularly important for a modern, computer controlled production environment, where very little human intervention is expected during the machining cycle. The accuracy of the probe, however, is affected by the machine tool positional accuracy and positioning system [10] and [11]. Since the same machine which produced the parts is used for inspection, there is an inherent problem in the accuracy of probe inspection. Therefore, in order for the probe data to be used for real-time control, the capability of probe needs to be analyzed and the factors affecting the probe data need to be ascertained.

The comparative study on the CMM and probe readings presented in this study is useful for today's manufacturing environment where diverse products are machined with ever decreasing lot size and minimal human intervention. The experiments conducted in this study simulated the batch mode manufacturing, using highly common industrial material types. Harder material (4140 steel) showed a much wider variation in the measurement difference between the CMM and the spindle probe; hence, care must be exercised if a feedback signal is to be used for correcting part size. For steel, it is believed that higher hardness increased the cutting force and the tool deflection in machining, which in turn caused a wider variation in the measurements. The error models using the ASVR techniques have a very high accuracy, suggesting that the spindle probe reading can be used for real-time, closed-loop control of part size. This, however, stipulates a gauge study to verify the magnitude of errors and the capability of on-line measuring instruments.