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Removable XYZ Alignment Jig for encoder module between code wheel and detector IC

IP.com Disclosure Number: IPCOM000244176D
Publication Date: 2015-Nov-19
Document File: 3 page(s) / 813K

Publishing Venue

The IP.com Prior Art Database

Abstract

This paper is to explain the concept of Removable XYZ Alignment Jig and its function to align radial position and gap between code wheel and detector IC in easier way It shows how effective the slider reduces customer assembly steps and cycle times

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1. Abstract

This paper is to explain the concept of Removable XYZ Alignment Jig and its function to align radial position and gap between code wheel and detector IC in easier way. It shows how effective the slider reduces customer assembly steps and cycle times.

2. Introduction

Encoder is an electro-mechanical device used to monitor and measure the position, rotation velocity and acceleration of the shaft in the application. Figures (a) to (c) below show various encoder working principles and their respective basic components. Basically, the device consists of an emitter as light source, lens, patterned code wheel/codestrip and an array of photodetectors and signal processor on detector IC. When the codewheel/codestrip moves between the emitter and detector, the light beam is interrupted by the pattern of bars and spaces on the codewheel/codestrip. Similarly, in reflective or imaging, the lens over the LED focuses light onto the codewheel/codestrip. Light is either reflected back to the lens over the photo-detector or absorbed by the codewheel/codestrip. As the codewheel/codestrip moves, an alternating pattern of light and dark corresponding to the pattern of the bars and spaces falls upon the photodiodes. The photodiodes detect these interruptions and the outputs are processed by the signal processor to produce digital signal. In order to obtain good signal for optimized encoder dynamic performance, the radial position of detector IC relative to code wheel pattern and the gap between the detector IC and code wheel must be aligned. Radial alignment is needed to ensure the code wheel pattern match with the PD pattern on detector IC. The gap between the detector and code wheel determines the optical contrast of the image formed by code wheel pattern. The nearer the gap, the better optical contrast is and the better dynamic performance of the encoder. However if the gap is too small, there is a risk of code wheel scratch during operation, especially when the code wheel wobble during rotation. As a result, the gap must be set accurately.

3. Current design #1

Figure 3-E and show the current typical design of encoder module. The code wheel assembly and detector module are two separated parts when shipped to customer. As a result, these parts occupy almost twice of the packaging space as compared to the size after fully assembled. Customer also needs to use 2 separate jigs for radial(using Centering Jig) and gap(using Removable Spacer) alignment purpose. A centering jig is used to align the radial position between Code Wheel and Detector IC, as illustrated in Figure 3F.

After the radial alignment and secured Base Plate by screws, customer needs to use a removable spacer to obtain desired gap between code wheel and detector IC as shown in Figure 3C. Cross-sectional view of Figure 3C shows in Figure 3G. Removable spacer with specific thickness is used as a temporary support area to code wheel. After fixed the position of code wheel to detector IC, hub...