Contact Based 3-D Scanning System for Non-Rigid Object Surface Measurement

[[abstract]]三維掃描器根據探測方式的不同，主要分為非接觸式和接觸式兩大類。非接觸式掃描掃描速度快，這類的掃描器大多利用光線對物體進行掃描，較不會損壞物件表面，但缺點為掃描反光或透光材質的物件，會造成掃描不佳或需要額外處理。接觸式掃描的量測準確度高且不受物面光學特性影響，缺點為量測速度慢。且在測量表面脆弱易變形的物體，易造成損害或者是量測不準確。因此，本論文以模組化設計一套接觸式掃描系統，以解決接觸式掃描器用於非剛性物件的問題。我們自行設計控制器模組，以轉譯電腦端下達命令為步進脈衝，並送至驅動器以控制步進馬達線圈的導電時序。接著我們設計探針感測模組，使用帶通放大器與比較器來放大壓電探針訊號，使得極小的接觸力可以被即時偵知而不會造成待測面的變形或破損。我們透過四個實驗來測試實作出來的三維掃描器精確度，驗證測量誤差在 0.01 mm 之內。也證實這個三維掃描器可以精準的重建果凍這種軟而易受損的待測物面的三維模型。雖然掃描時間較長，但掃描精準度遠勝於一般雷射掃描器。[[abstract]]Existing 3-D scanners can be classified into contact-based scanners and contactless scanners. Contactless scanners uses light sources and image sensors to measure the object surface and, therefore, it is fast and safe to measure most object surfaces. However, it is not suitable for object surfaces with specular reflection property or transparency. Conversely, contact-based 3-D scanners are generally accurate and suitable for objects with different kinds of optical properties. The drawbacks of the contact-based scanners include slow measurement speed and are not suitable for deformable and/or fragile surfaces because the probe may cause surface deformation or even damage the object surface. In this thesis, a contact-based 3-D scanner is developed to solve the problem of scanning deformable and/or fragile surfaces. Controller modules are designed to convert high-level command from computer to stepper motor driving pules. The driving pules are send to a stepper motor driver that controls the conducting timing of the stepper coils. We have also designed a probe sensing module which includes a band-pass amplifier and a comparator to process the signal from a piezo sensor. This module can detect tiny contact force which prevents any deformation or surface damage due to probe contact. Four experiments are contacted to test the accuracy of the developed 3-D scanner. The experimental results show that the measurement error is below 0.01 mm. We also show that the 3-D scanner can be used to scan the surface of a jelly without causing any damage to the jelly surface. Although the scanning speed is slow, the developed system can achieve much higher accuracy than general laser 3-D scanners.[[note]]碩