LBTO PMC Subsystem

February 13, 2007

Chris Biddick

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Introduction The PMC controls the primary mirror position and

figure (shape) Gets commands from the GUI and PSF Sends command to the ECS Essentially finished Reference Documents

• 481s041 PMC Reference Manual• 481s042 PMC User’s Manual• 481s043 Actuator Firmware Reference Manual• 481s044 Hard Point Firmware Reference Manual• 481s045 PMC Thermal System Description

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Components

Hardware• Actuators

• Hard points

Software • Firmware

• Real time

• Subsystem

• GUI

Mirror cell nomenclature (1) ‘Actuator’

• A one or two axis pneumatic device for applying force to the back of the mirror – 160 per cell

‘Hard point’• An almost magical mechanical/pneumatic device for

determining the position of the mirror – 6 per cell• Measures force and position• Has a stepper motor to change length• Is stiff until the force is too high, when it collapses or

extends to avoid damaging the mirror ‘Breakaway’

• What a hard point does when the force on it is too high

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Mirror cell nomenclature (2) ‘Magic position’

• Position where mirror travel is approximately centered

• Becomes the mirror coordinate system origin ‘Panic’

• What happens when VxWorks determines that a seriously bad or unsafe condition exists• The air pressure is allowed to bleed off so the mirror settles

down on the static supports

‘Static supports’• Small wire “baskets” with an attachment bolt that hold the

mirror in the cell when the actuators are not active – 426 per cell (one per puck)

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Mirror cell nomenclature (3) ‘Load spreader’

• One, two, or three puck frame that attaches an actuator to the mirror

‘Puck’• An attachment pad glued to the mirror or glass wedge

‘Glass wedge’• A glass piece glued to the mirror that provides the

attachment point for hard points ‘Outer loop’

• PI feedback loop calculated in software to minimize the hard point forces and moments – 6 per cell

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Mirror cell nomenclature (4)

‘Raise’• The process of gradually applying actuator

forces to the mirror to bring it off the static supports and to the magic position

‘Floating’• When the mirror is fully off the static supports

‘Lower’• The opposite of raising

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Mirror cell nomenclature (5)

‘Chasing’• Moving the hard points while keeping their

forces near zero and either• Keeping the actuator forces constant (outer loops off)

• Allowing the actuator forces to change (outer loops on)

‘Outer count’• A pitiful kluge to reduce the effective feedback

gain in the outer loops to help avoid mirror oscillations (no longer used)

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Mirror cell nomenclature (6)

‘Elevation feed forward’• Using the mount elevation angle to improve the

response of the outer loops as the telescope changes elevation

‘Ventilation’• The process of blowing air into the back of the mirror

to control its temperature

‘Zernike coefficients’• Coefficients of polynomials describing optical

distortions

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Software (1)

The PMC is composed of several programs running on different computers

Real time software• Actuator and hard point control firmware

• Written in C, compiled on Windows

• Runs on PIC 18F252 processor

• VxWorks – real time control of entire cell

• Written in C, compiled on Windows

• Runs on PowerPC 7410 VMEbus system

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Software (2)

Linux software• Thermal data readout

• Written in C

• Runs on thermal computer (PC in lower left tree house)

• PMC subsystem

• Written in C++

• Runs on TCS server

• PMC GUI

• Written in C++ (QT designer)

• Runs on TCS TO station

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Firmware

Provides serial port communication and status for actuators and hard points

Provides local force feed back control on actuators

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VxWorks (1)

Communicates with the firmware over serial ports, has digital outputs for air pressure and hard point control, and analog inputs for air pressures and voltages

Communicates with PMC using TCP sockets

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VxWorks (2)

Controls• Individual actuator forces

• Individual hard point motors

• Air pressures

• Mirror position

• Forces and moments (outer loops)

• Mirror figure changes

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VxWorks (3)

Status• Actuators

• Air pressure sensors

• Errors

• Forces and moments

• Hard points

• Position

• Outer loop data

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VxWorks (4)

Performs safety checks on forces and moments

Provides various special commands through a telnet interface

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Thermal computer

Reads cell thermocouples and thermistors, converts to degrees C• Takes about 50 seconds

Runs one server process for each cell• Returns last data read when asked

Also runs ECS thermal readout

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Subsystem (1) Nine threads for VxWorks

• Actuators – 21 commands, status at 5 Hz• AirPressure – 4 commands, status at 4 Hz• AsyncMessages – 0 commands, status at 4 Hz• Hardpoint – 3 commands, status at 37 Hz• Mirror – 20 commands, status at 3.33 Hz, sends

elevation angle at 10 Hz• Motor – 7 commands, status at 4 Hz• PMC – 6 commands, status at 4 Hz• PMCLogger – 0 commands, status at 4 Hz• ServoLoop – 11 commands, status at 4 Hz

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Subsystem (2)

One thread for thermal computer• 1 command, status at 0.1 Hz (only changes

every 50 seconds), sends computed ventilation temperature set point to ECS at 0.1 Hz

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PSF requests

Move to position Stop move to position Load new figure forces Clear figure forces

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