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Controls for P olarimeter Converters. Brianna Thorpe Arizona State University. What are we doing?. Experiments 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: - PowerPoint PPT Presentation
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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
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