# Dimensional Control of Aircraft Transmission Bodies Using CNC Machines and Neuro-Fuzzy Systems
## 1 Introduction  
The article deals with the selected aspects of quality control of aircraft accessory drive train (ADT) bodies (Figure 1). In the case of the most responsible elements of aircraft construction, such as engine and transmission components, all manufactured items are checked. Due to the required accuracy of workpieces, dimensional and shape characteristics are obtained using coordinate measuring machines (CMM) (Figure 2). Due to their versatility, they currently constitute standard solutions for determining the dimensional and shape characteristics of aircraft transmissions. The biggest drawback of this type of approach is the high cost of purchasing and maintaining CMMs and long measurement time. Therefore, the measuring laboratory is very often the so-called bottleneck of the production process, because usually one CMM machine is used to serve several lines of machine tools. It should be noted that not all measurements must be performed with the same high accuracy. An alternative to some measurements made with CMMs are measurements made using CNC machines [1]. A set of measuring probes has been standard equipment for CNC machining centers for several years. Probes have a measuring element, called the stylus, which has a properly configured shape that enables the measurement of selected geometric quantities. In addition, the CNC machine has dedicated software and a receiver cooperating with the probes, enabling it to take relevant measurements and save the results in the form of CNC system variables or measurement reports. The control of bodies using traditional methods with the use of sensing devices and special gauges is labor-intensive and expensive due to the need to develop and produce the so-called testers, which are specific to a given design. Such equipment is intended for a particular body and can rarely be adapted to check other parts. In addition, this method of measurement is susceptible to the so-called human factor which causes errors. It also does not allow automatic generation of measurement reports. The paper presents the problem of determining a selected dimensional characteristic in such a way that the participation of CMM in the measurement process is as small as possible [2]. In the case analyzed in the article, it is not possible to completely eliminate measurements on CMM and replace them only with measurements on a CNC machine. Additionally, in the machining center, the shape-dimensional characteristics are determined in the mounted state, while in the measuring laboratory the characteristics are determined in a free state. This introduces a significant difference in the results of measurements resulting not only from differences in CMM and CNC machine accuracy, but also from deformation of the body after unmounting. The measure of these deformations is the curvature of the selected surface of the body. The paper presents a method for determining bearing seat position deviation based on measurement on a CNC machine and measuring the curvature of a surface on a CMM machine, using neuro-fuzzy models describing the relation between dimensions in the mounted state and free state. This approach allows the reduction of the number of characteristics determined on the CMM, and thus a smaller load on the measuring laboratory. The issue presented in the article has been developed for the needs of Pratt & Whitney Rzeszow. Figure 2(a) shows the current course of operations in the production of bodies, while Figure 2(b) shows the course taking into account the new solution developed. Figure 1: Aircraft engine with accessory gear (ADT). Figure 2: Coordinate Measuring Machine (CMM). If the number of measurement characteristics k determined on the CMM is much smaller than all the necessary characteristics m, then the solution presented in Figure 3b eliminates the bottlenecks problem and it is economically rational [3]. The necessary condition is the ability to build such computational models that enable the creation of a reliable measurement report.