PowerPoint Presentation

1Brianna ThorpeArizona State UniversityControls for Polarimeter ConvertersWhat are we doing?2Experiments at Jefferson Lab use controls for polarimeter converters

This minimizes problems in the experiments

We want to make a cheap, simple to use control

This will require:

Developing hardware

Writing software

Converter Issues: Electron Scatter

3What is this?

As an electron moves through the source, it bumps against other atoms. Why is this an issue?

As the thickness of the source increases, the ratio of scattering centers to electrons detected increases. Converter Issue: Delta Rays4

What is this?

As an electron travels through the source, it bumps against other atoms. This knocks off other electrons. Why is this an issue?

These other electrons (Delta rays) hit the detector at angles different than the recoil electron. Because both have similar kinematics, we have no way of knowing which is the recoil electron.

Converter Issues: Our Solution5The Solution: make the target (converter) really thin.

Our converter three different sources:

Beryllium Slightly thicker BerylliumCarbon

6How Do We Control the Converters?

7

Distance in beam direction between converter and detector is 35 mm8

Detector supports attached to plate with screws 9

Rack guide supports attached to plate with screws The Converter Control10

Motor

The motor moves the converter tray.

Control the motor and you control the converters.CarbonBerylliumThicker BerylliumConvertersStep One: The Hardware11We want cheap and simple:

Arduino: Open source electronics

Works with Linux

Programs written in C or C++

Lots of example code on the internet

Cost: $99

12

Motor shieldMicrocontrollerThe Arduino board is our microcontroller

Our code tells the Arduino what to do

The Arduino relays our commands to the shieldsShields: Electronics that are stacked on the microcontroller

Our motor shield speaks to our motor

Cost: $27

Our Ethernet shield allows for Ethernet communication

Cost: $35

Ethernet Shield13Hardware Issues:

The Arduino motor shield had a pin conflict with the Ethernet shield

This prevented communication between the shields

Our Solution:

An inexpensive pin-reassignment shield

We used solder to reassign the pins

14

We hooked our stacked Arduino and shields to a cheap test motor

Bipolar

200 steps per revolution

12 Volt

Cost: $20 (including shipping)

Step Two: The Software15

Installed on lc64 Linux box

Installed on my Windows laptop

Used example code for testing.

The code for Arduino is called a sketch

Compiled using Linux and Windows. We are fully platform independent. 16

The code to control the motor was written in the Arduino program.

The Graphical User Interface was written in Vpython. The GUI allows for communication between the sketch and the ArduinoGUI Position: retracted17

18GUI Position: One

19GUI Position: Two

20GUI Position: Three

Application at Jefferson Lab21

The GUI will live hereCost Effectiveness22

Controller: $595Controller chassis: $4750

Total Cost: $181Total Cost: $5345Putting it all Together23

The Finished Product24

Acknowledgments Dr. Mike DuggerDr. Barrie RitchieRoss TuckerTodd HodgesBen Prather252627Converter Stick assemblyColor code: 1.5 mm thick 3.0 mm thick 1.4 mm thick

Material: AluminumAll units in mmHole 1-3: 8x8Hole 4: 8x42Screw holes on converter tray are threadedWeight ~ 0.41 oz

Hole 3Hole 2Hole 1Hole 411116161616113316822426722Converter trayConverter plate28Converter retracted

Mounting plateRack stopRackRack stopConverter trayConverter legDetector cardTeeth on rack not shownConverter tray 11 mm from beam centerConverter tray detail shown later11 mm29Converter position 1

102 mm176 mm5 mm10 mm30Converter position 2

31Converter position 3

32Different view

33Front view

3 mm10 mm10 mm34View from downstream, detector removed

Weight of rack ~ 0.97 ozWeight of arm ~ 0.26 ozWeight of converter tray assembly ~ 0.41 oz

Weight of rack+arm+converter tray assembly = 1.64 oz91 mm35Gear added

Gear has outer diameter of 15 mm (can be a bit smaller) with a minimum of 18 teeth

Teeth on gear not shown

Precision in linear motion per step (200 steps per revolution is standard for stepper motors): ~1/4 mm

36Rack guide added

If rack guide is aluminum then coefficient of static friction between rack and rack guide is between 1.05 and 1.35. Using 1.35 as conservative estimate of coefficient of static friction, then the force needed to break static equilibrium is 1.35*1.64 oz ~ 2.2 oz 37Motor added

Since gear has radius of 7.5 mm (~ 0.3 inch) and force needed to break static friction is 2.2 oz, then minimum torque required of motor is ~ 0.7 oz-inch

Motor that Im interested in has holding torque of 7.5 oz-inch

Motor details shown later.

38Motor mount added

Motor mount attached to plate with screws (not shown)

Want two cm clearance between upstream chamber wall and motorUpstream