Accurate modeling and prediction of surface roughness by computer vision in turning operations using an adaptive neuro-fuzzy inference system

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Abstract

Modeling and prediction of surface roughness of a workpiece by computer vision in turning operations play an important role in the manufacturing industry. This paper proposes a method using an adaptive neuro-fuzzy inference system (ANFIS) to accurately establish the relationship between the features of surface image and the actual surface roughness, and consequently can effectively predict surface roughness using cutting parameters (cutting speed, feed rate, and depth of cut) and gray level of the surface image. Experimental results show that the proposed ANFIS-based method outperforms the existing polynomial network-based method in terms of modeling and prediction accuracy.

Introduction

Standard roughness measurement procedures depend heavily on stylus instruments which have only limited flexibility in handling different parts. Furthermore, the procedure is a post-process approach, which is not amenable for automation, and the measurement is also relatively slow. In recent years, the modeling and prediction problems of surface roughness of a workpiece by computer vision in turning operations have received a great deal of attention [1], [2], [3], [4], [5], [6]. Although it has been shown that the surface roughness is strongly characterized by the surface image, practical surface roughness measurements based on computer vision technology are still difficult [1]. The main problem is how to accurately obtain the actual surface roughness of a workpiece using surface images and various parameters of cutting operations. Lee and Tarng [1] used a self-organizing adaptive learning tool called polynomial network (PN) [7] to establish the relationships between the actual surface roughness of a workpiece and the feature of surface image under a variety of cutting operations. As a result, the PN-based method can effectively predict the surface roughness with reasonable accuracy. The reported mean error of prediction of surface roughness is about 6.2%.

To improve the accuracy of predicting surface roughness, this study uses a more powerful learning tool called fuzzy neural network (FNN) [8], [9], [10] to solve the problems of modeling and prediction of surface roughness. It is known that the adaptive neuro-fuzzy inference system (ANFIS) is efficient for non-linear mapping. ANFIS is a fuzzy inference system implemented in the framework of an adaptive FNN. By using a hybrid learning procedure, ANFIS can construct an input–output mapping based on both human knowledge (in the form of fuzzy if–then rules) and stipulated input–output data pairs [8], [9]. In this paper, we utilize ANFIS to model the relationship between the features of surface image and the actual surface roughness. Consequently, once the cutting parameters (cutting speed, feed rate, and depth of cut) and gray level of the surface image are given, surface roughness can be accurately predicted. Using the same group of surface images and turning parameters as that in [1], the average errors of modeling and prediction are 5.88×10−8% and 0.38%, respectively. The encouraging experimental results show that the proposed ANFIS-based method outperforms the existing PN-based method [1] in terms of modeling and prediction accuracy.

Section snippets

Computer vision system for inspecting surface roughness

For comparison with the PN-based method [1], the same group of surface images and turning parameters is used in this study. The computer vision system for inspecting surface roughness adopted by Lee and Tarng [1] is briefly described as follows. The schematic diagram of the computer vision system including a vision system with a digital camera (Olympus C-1400L) and an appropriate lighting arrangement is shown in Fig. 1. The camera captures surface images with 1280 × 1024 resolution, 1/30 s

The proposed ANFIS-based method

The architecture of the ANFIS used in the proposed method is shown in Fig. 2. There are four input parameters (V, F, D, Ga) and one output value, the predicted surface roughness Ra. Denote the output node i in layer l as Ol,i. The used five-layer ANFIS is described as follows:

Layer 1: Every node in this layer is an adaptive node with a node output defined: O1,i=μvi(V), for i = l,…, m, O1,i+m=μFi(F), for i = l,…, m, Ol,i+2m=μDi(D), for i = l,…, m, O1,i+3m=μGai(Ga), for i = l,…, m, where V (or F,

Modeling and prediction of surface roughness

The experimental data of 57 turning experiments listed in Table 1 are utilized to train the used ANFIS model with m = 3. The hybrid batch learning rules are used in the training [8], [9], [10]. The values of premise and consequent parameters obtained after training are given in the Appendix. The trained ANFIS establishes the relationship between the features of surface image and the actual surface roughness. Once the cutting parameters (V,F,D) and the gray level Ga are given, then the predicted

Conclusion

This paper proposes a method using an adaptive neuro-fuzzy inference system (ANFIS) to accurately establish the relationship between the features of surface image and the actual surface roughness, and consequently can effectively predict surface roughness using cutting parameters (cutting speed, feed rate, and depth of cut) and gray level of the surface image. The advantages of the proposed method are non-contact measurements, ease of automation, and high accuracy. Experimental results have

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