Lexmark Rotary Shaft Encoder

Team members: Scott Blakely

Jeff Clover Luke Spicer

Kurt Thomas Dustin Webb

Review project objectives and system requirements

Background and derived requirements

Static test results

Conclusions drawn

Dynamic test results

Conclusions and part recommendations

Summary

Overview

Characterize the reflective approach with multiple devices and a variety of films and substrate materials on the encoding disk

Carefully control the emitter/detector array to encoding disk spacing during testing

Optimize the reflective design to achieve the best performance at the lowest cost possible

Project Objectives

Previous Transmissive Approach

http://www.avtron.com/images/jpgs/optical-encoder.jpg

http://www.avtron.com/images/jpgs/optical-disk.jpg

Converts shaft angular position to an analog electrical output

Output is used to determine shaft angular position, RPM, etc.

Opto-Reflective array is used to produce the analog electrical output

Reflective Operational Concept

Diagram courtesy of previous UofL CAPSTONE Group

IR LED

Photo Transistor

Encoding Disk

Input 24 VDC motor power, 5 or 3.3 VDC, and Ground

Output High ≥ 2.2 VDC; Low ≤ 0.6 VDC

Pulse width ≥ 17 μsec

Motor Speed Max ≈ 6000 +/- 150 RPM; Min ≈ 200 RPM

Size of PCB Length = 37.0 mm, Width = 30.5mm, Height = 14.0mm

All materials must adhere to UL Material Flame Class 94V0

System Requirements

Data sheets show for sensor to be most effective:

Industry Standard = 1mm from encoding disk

Optimal range = 0.6 ≤ x ≤ 0.8 mm

Similar graph for Fairchild and Sharp

Derived Requirement

Figure from OSRAM SFH 9201 data sheet.

Test Fixture

Designed based around moving the sensor instead of the disk

Calipers chosen based on level of accuracy and price

Modeled in SolidWorks

Screwing components used to move the calipers in small increments

Test Fixture

Can measure +/- .02mm

Vertically adjustable

Fixture was rapid prototyped

Rubber band acts as a retracting mechanism

Allows for the disk to be stationary by moving the sensor to and from the disk while motor is running.

Secured so the sensor is parallel to disk.

We tested multiple sensors from each company (Sharp, ORSRAM, & Fairchild)

Incremented the spacing between opto-reflective array and encoding disk to find optimum range

Noted reproducibility characteristics for each sensor and compared normalized data

Static Testing

Fairchild Static Test Results

Normalized Fairchild Data

Verified Ic/Imax vs. Distance curves from datasheets

Fairchild is the overall favorite Performance

Reproducibility

Cost Reduction

Front runners for encoding disk design 8-window PCB with copper

8-window photo paper

On to dynamic testing!!!!

What we know now

Dynamic Testing

8-window versions

PCB with copper plating

White paper

48-window versions

PCB with copper plating

White paper

Test Combinations

64-window versions

PCB with copper plating

Stamped Aluminum

Sputtered Gold

Black Nylon

White Painted

Fairchild QRE-1113 #1 8 Window Disk PCB Substrate Bare Copper Surface

Speed = 6,000 RPM

2.2 Volts

0.6 Volts

540 μs High Time Pulse Width

570 μs Low Time Pulse Width

*5 VDC Applied

Fairchild QRE-1113 #1 8 Window Disk PCB Substrate Bare Copper Surface

Speed = 200 RPM

2.2 Volts

0.6 Volts

25 ms High Time Pulse Width

20.4 ms Low Time Pulse Width

Fairchild QRE-1113 #3 48 Window Disk PCB Substrate Bare Copper Surface

Speed = 200 RPM

2.2 Volts

0.6 Volts

1.36 ms High Time Pulse Width

1.48 ms Low Time Pulse Width

*5 VDC Applied

Fairchild QRE-1113 #3 48 Window Disk PCB Substrate Bare Copper Surface

Speed = 6,000 RPM

2.2 Volts

0.6 Volts

*Signal did not meet requirements *5 VDC Applied

Fairchild QRE-1113 #3 8 Window Disk White Paper

Speed = 6,000 RPM

2.2 Volts

0.6 Volts

560 μs High Time Pulse Width

470 μs Low Time Pulse Width

*3.3 Volts Applied

Fairchild OSRAM Sharp

64 PCB w/ Cu X X X

White Painted X X X

Stamped Al X* X* X*

White Paper X X X

48 PCB w/ Cu X* X* X

White Paper X* X* X*

16 PCB w/ Cu √ √ √

White Paper √ √ √

8 PCB w/ Cu √ √ √

White Paper √ √ √

Summary of Dynamic Results

* Indicates signal did not meet max RPM requirements

Opto-reflective array to encoding disk spacing

From static tests, ideal spacing ≈ 0.7 +/- 0.1 mm

Can still see clear useable signal out to 1.2 mm

Best sensor

Fairchild outperformed Sharp and OSRAM during dynamic testing

Best encoding disk

8 & 16 window Copper PCB

Conclusions

Power Supply

We were able to meet requirements at 5 VDC and 3.3 VDC using best combination of sensor/disk

64 window designs did not meet all requirements

Suggestion for further study:

Study the effects of window width in higher window designs

Study the effects of life testing and aging of opto-reflective array

Conclusions (cont’d)

Prototype

Reviewed project objectives

Reviewed system requirements and primary derived requirement

Improved Test Fixture

Static testing showed us optimal spacing

Dynamic testing showed us best combination of sensor array and encoding disk

Summary

Questions?

OSRAM Static Test Results

Normalized OSRAM Data

Sharp Static Test Results

Normalized Sharp Data

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Ic/Imax

Distance (mm)

Sharp GP2S24J0000F #2

Aluminum

Black Nylon

Copper

Gold

White Nylon

White Painted

White Paper

Material

Fairchild QRE-1113 #3 8 Window Disk White Paper

Speed = 6,000 RPM

2.2 Volts

0.6 Volts

460 μs High Time Pulse Width

510 μs Low Time Pulse Width

*5 VDC Applied