1. ZTF Filter Exchanger Controls System
D. Hale

2. FILTERD FILTER HARDWARE
context of where the next two hardware slides fit in

3. Software Interface to Hardware
KUKA Arm
TCP/IP socket interface to arm controller
commands to and status from controller are transmitted as XML strings
status thread is responsible for the I/O function calls

4. Software Interface to Hardware
Arduinos
control Electro-Permanent Magnetic (EPM) latches
read EPM states
read mechanical latch micro-switch states
A dedicated Arduino-based microcontroller monitors sensors at each of these physical locations:
instrument
gripper tool
four filter storage slots
Arduino Interface
A master Arduino handles communication between the Robotic System and each of the six host Arduinos
TCP/IP socket interface to master Arduino
I2C communication between master and host Arduinos
status thread is responsible for the I/O function calls

5. example
command
context of where the following slides are going to fit

6. Commands
There are many possible commands that can be recognized by the command thread
e.g. exchange_filter(N), stow, instrument, slot, etc.
The building blocks of all commands are “primitives” which interface to hardware
rigorous unit testing of primitives ensures system reliability

7. Primitives KUKA Arm Primitives EPM Primitives Sensor Primitives stow
slot( N )
instrument
check_handoff
EPM Primitives
engage
disengage
Sensor Primitives
check values
These describe all arm movements as specific, pre-defined paths
No arbitrary motions means less room for error and more control over safety
turns the magnetic latches on and off

8. Example Command Operations: Check_Status Retrieve Undock Store Dock
Fetch
Install
Stow
NB. discrepancy between flowchart boxes and operation list is closet dock/undock not shown

9. 8. Install
instrument primitive moves gripper tool carrying filter frame to the instrument
EPMs=on and reading no filter
latches closed
EPMs=on and reading filter
describe what’s going on with the sensors

10. 9. Dock EPMs=on and reading filter EPMs=on and reading filter
latches open
EPMs=on and reading filter
EPMs=off
describe what’s going on with the sensors

11. 9. Dock check_handoff moves arm a safe distance
mechanical latches maintain control until handoff complete, in case of EPM or pawl failure
EPMs=on and reading filter
latches closed
EPMs=on and reading no filter
describe what’s going on with the sensors

12. How are Faults Handled?
For every Operation there is defined a set of sensor values required for success
Fault / Response / Action table
a violation is a fault
fault handling is situationally dependent

13. Fault / Response / Action table
Here’s the entire matrix – many possible fault responses and actions to take

15. Safety The KUKA arm has inherent fault protection and safety features
velocity monitor
limits kinetic energy
workspace monitor
limits motion to a defined workspace volume
axis range monitor
angular limits
collision monitor
force/torque sensors on each joint

16. Emergency Stop deactivates drive power and applies brakes
trigger sources:
strategically placed panic buttons throughout dome
door switches
telescope tube access doors, filter storage closet doors, etc.
limit switches installed on arm

17. External Limit Switches & Hard Stops
hard-stop barriers & limit switch affixed to upper side of axis
block affixed to lower side of axis
allows some rotation
first within boundaries of switch
ultimately within hard-stop boundaries

18. Conclusion control software successful heritage with Robo-AO
modularity of the design facilitates testing
sub-system testing of lab mock-up will validate operation and fault handling
KUKA advantage of mature commercial product
local JPL collaborative experience