內螺紋自動檢測機台之設計研發

Abstract

內螺紋（Internal Thread）自動化攻牙製程雖已行之多年，但仍會發生異常狀況，最 常見的問題為螺紋攻出器（Screw Taps）的磨損太大，導致加工後的內螺紋數量不足、 螺距狹窄、螺紋山形狀不佳，甚至完全無法製成螺紋。為維持內螺紋之品質與功能性， 業界常以螺紋塞規（Thread Plug Gauge）反應內螺紋的中徑、螺距和螺紋山角度的精度； 然而，使用螺紋塞規必須面臨許多接觸式檢測（Contact Inspection）固有且不可避免的 缺點。因此，為了適應大批量生產且滿足自動化的需求，勢必要導入非接觸式的檢測 （Non-contact Inspection）技術。本計畫的目標在於提出以機器視覺（Machine Vision） 為基礎的內螺紋非接觸式檢測方法並開發一種針對內螺紋進行檢測的機具，其主要的精 神為建構一光學式螺紋塞規（Optical Thread Plug Gauge )，計畫中將引入工業用內視鏡 （Industrial Endoscope）、電荷耦合元件（Charge Coupled Device，CCD）與馬達控制單 元（Motion Control Unit），並發展一新的圖像拼貼法（Unwrapped Method）建立內螺紋 孔壁的全周圖像（Hologram），接著，再從全周圖像的特徵中，找出可用於辨識或檢測 螺紋品質的資訊。本計畫所提出的內螺紋自動檢測機制將能夠自動地判別螺距是否正 常、螺紋山是否受損、螺峰、螺谷的邊界是否平滑、是否尚有攻牙製程的殘留料屑等問 題。囿於內螺紋特殊的結構與空間的限制，目前尚未見到以機器視覺進行自動內螺紋檢 測的文獻。透過本計畫特殊設計的取像機制，將可解決內螺紋深度與孔徑尺寸所帶來的 取像困擾，並可在大批量生產環境之下，提供快速且自動化地綜合性檢測；而所研發的 內螺紋自動檢測機台亦能用於內螺紋製程中，當螺紋攻出器產生過度磨耗或出現斷裂等 異常現象之初，就能及早發掘問題的徵兆，並給予操作員適時的警報訊息，進而使產品 品質穩定與節省成本。

Although the tapping process of internal thread has been automatized, some exceptional conditions still arise. All too often, a damaged screw tap may shape nonconforming threads. To preserve the quality and functionality of internal thread, a thread plug gauge is used to reveal the precision of pitch diameter, thread pitch and lead angle. However, manual and contact inspection causes various inherent and invertible persecutions. Therefore, industry should introduce automatic and non-contact inspection method to satisfy the environment of mass-produce. This project is to propose a novel internal thread inspection mechanism by machine vision. The main purpose is to construct an optical thread plug gauge. To do so, partial wall image of internal thread captures by elegantly cooperating and guiding the rigid industrial endoscope, CCD camera and motion control unit. An unwrapped image method can then be reconstructed the hologram of internal thread. Next, some crucial features would be extracted to identify the quality of internal thread. The developed optical thread plug gauge would be capable of distinguishing the thread pitches, the thread flank, the thread crest or root and residual material filings. Consequently, the novel method can provide high-speed, composite and automatic inspection in mass-production environment. It can send an alarm signal to the operator when the screw tap was over-weared or broken down such that the industry can achieve the goal and a stable product quality and save cost.