LHC Collimation Project
Integration into the control system
Michel Jonker
External Review of the LHC Collimation Project
1 July 2004
LHC Collimation system
• Up to 120 collimators
including tertiary, scrapers, absorbers, phase 2, etc
• Distributed over 6 points with a large concentration in
point 3 and 7
• Jaw positions are
correlated
primary – secondary –
tertiary
Also during movements!
they have to stay in sync
Collimator control
A single collimator has
• 5 stepper motors
• 5 resolvers (position measurements
coupled to the motor axes)
• Other position measurements
– Potentiometers
– LVDT’s
• Operational condition sensors
–
–
–
–
–
Temperature gauges
Water pressure
Water flow
Accelerometers
Audio recorder
Local Collimator Control
• Stepper motor control
• Position readout and survey
Under study:
• PLC or
• Integrated electronic system
• Readout of other parameters
• May include the redundant position
measurements.
• Generation of beam dump signal
• PLC
Local position
control
• Position Control
Position Control System
subject of a market survey
A position control system assembly
• controls multiple motors (up to 100 per assembly)
• may be either:
– A PLC based system
Responsibility for the development of PLC software should be part of the market survey.
– An integrated electronic control system (e.g. like in LEP)
In either case we need:
– a communication interface with the system based on the modbus protocol (or
equivalent). I.e the assembly looks like a PLC.
– to have the right and the support to modify embedded software.
(I.e. have the possibility to in-source the maintenance.)
The real issues here are:
– Low electric noise in motor control (no chopper supplies)
– Control over long distances
Collimator Control Architecture
Control Applications
Feedback
Application
Beam Loss
Signals
Central Collimator
Control
Beam dump
.....
Local position
control
Timing distribution
Modbus on Ethernet
Local position
control
Setting Database
Modes of operation
Based on various operational scenarios
Used to define functional requirements
a) Without beam present
•
Unsynchronized movements
b) With beam present
•
•
Synchronized & position-surveyed movements
Unsynchronized fine adjustments of individual collimator
jaws
Modes of operation
Unsynchronized movements
• When
No beam present
–
Position calibration procedures
–
Prepare for injection
• No global synchronisation required.
• Both sides of a jaw have to remain within 1 mm
–
Is the responsibility of local position control
Mechanical speed limit: < 10 mm/s
•
Time to detect problems 100 ms (is acceptable)
Modes of operation
Synchronized position-surveyed movements
• When
Beam present
–
Movements during the ramp or during the squeeze
• Global synchronisation required (movements start at the same time)
• Detection of positioning errors during movements.
–
–
Maximum tolerable error may vary (can be as small as 25 m)
Drive speed limit = max error / system response time
E.g. 25 m / 100 ms = 0.25 mm/s
In case this is in the resonance range of the assembly, the speed should
be further reduced. (Continuous single step mode).
Modes of operation
Unsynchronized fine adjustments (individual jaws)
a)
b)
•
Under control of the operator
Driven by feedback from beam-loss systems
When
Beam present
•
At injection, the end of the ramp, or in preparation of physics
•
•
•
•
No global synchronisation required (mostly one or two
motors per command)
Commands to move by a few (1 – 5) steps at the time
Command rate up to 10 Hz (feedback driven)
Speed: a few times 50 m/s
Functional Requirements
Motor Control
• Controlled by preloaded movement functions:
– Movement functions are triggered by a common
hardware or software signal (common to the assembly).
– Movement functions can be simple or complex.
• Simple functions are used for tweaking collimator positions.
• Complex functions for calibration, ramp
Functional Requirements
– Examples of movement functions
Simple function
• start condition,
• time, displacement
• stop condition
Displacements are either absolute or relative
Complex function
• start condition,
• n x { time, displacement}
• Stop, pause, conditions
Displacements are either absolute or relative
Functional Requirements
Motor Control (cont.)
• Movements are interruptible by external stop signals (hardware and/or
software)
• Actual motor position can be re-initialized.
• External hardware conditions are recorded by the system and are
reported to the supervisory system.
• The theoretical positions can be read at any time by the supervisory
system.
• The system maintains a history in terms of executed motor steps. The
history is kept in non volatile memory. (Post mortem analysis)
Functional Requirements
Resolver Readout
• Autonomous readout and position error detection by the
system:
– The system continuously measures and compares, independent of a
supervisory system.
– Position errors are signalled by HW output signals and by software reports
to the supervisory system. (different error thresholds?)
• Acquisition and position error detection is also active
during movement:
– Needs to receive functions that specify position and tolerance.
– Needs to receive time synchronisation signals (to follow motor control
functions)
Functional Requirements
– Error thresholds vary during movement (they are more strict
when closer to the beam)
– Error thresholds can be asymmetric
• Can be represented by a minimum and a
maximum bound function.
– Use similar function format as for motor control
Functional Requirements
Resolver Readout (cont.)
• sampling speed (adjustable?)
– @ 50 ms: 14 bits = precision 2.5 um (40 mm /16384)
– @ 10 ms: 13 bits = precision 5 um (40 mm / 8192)
• The resolver readout system uses same hardware start and stop signals
as the motor control.
• The actual positions can be read at any time by the supervisory system.
• A history is kept in non-volatile memory for post mortem analysis.
Central Collimator Control
• Provides a ‘standard equipment’ view
to the LHC control
Feedback
Beam Loss
Control
Applications
Setting Database
system.
Application
Signals
– Accepts command
ramp
Central
Collimator
Central for
Collimator
Control
– Accepts actual setting
trims.
Beam dump
– Coordinates the movements between the individual collimator
Timing distribution
assemblies.
Modbus on Ethernet
– Reports changes to the application layer for logging.
.....
Local position
control
Local position
control
• Listens for error reports and acts on them.
• Acts as a gateway to relay FB information from the Beam
Loss systems to the local position control systems.
• Implemented on a VME system running LynxOs
Conclusions:
Local Collimator Control
Readout of collimator operational conditions does not pose
any problem (PLC based).
Details of the local architecture still uncertain due to the
uncertainty of the local motor control system.
– There is one potential candidate that may provide an integrated electronic
assembly. (Based on the electronics for the Lep System)
– There are possibly many PLC based solutions but which needs to
demonstrate their capability to comply with the low electric noise
requirements.
– Essential points
•
•
•
•
Low electric noise, long distances
Function driven motor control
Position Acquisition: precise, fast, autonomous, including position error detection
capabilities
Post mortem history buffers.
Conclusions:
Central Collimator Control
• Functionally very similar to other LHC equipment.
• Based on common LHC control architecture.
Phased implementation ?
– Simple setting control for day 1
– Use of functions and position survey during movements
– Feedback based on beam loss signals
However, all these modes of operation have to be foreseen
in the control system right from the beginning.