REVISION Control stuff Flashcards Preview

3P2 HUGO > REVISION Control stuff > Flashcards

Flashcards in REVISION Control stuff Deck (50):
1

What are the different aspects of operation automation?

What aspects of an operation to automate?

 

SENSE: info gathering

 

ANALYSE with REQUIREMENTS then

 

DECIDE: generate decision operations and selections which guide operation

 

ACTUATE: provide automatic or guided manual support

 

OPERATION

A image thumb
2

Define automation

Definition of Automation – the part or full replacement of human based functions with a machine, computer or other device

3

What makes automation hard?

What makes automation hard?

  • Complex logic
  • Concurrent operations
  • Constraints e.g. Limited resources
  • Many different operating patterns
  • Human interfacing

4

What are the downsides of automation?

What are the downsides of automation?

  • Cost
  • Complexity
  • Flexibility
  • “Experience effect”
  • Un-noticed errors
  • Job losses
  • Trade off in balancing benefits/downsides

5

What are the reasons for automation?

What are the reasons for automation?

 

  • Labour productivity
  • Speed
  • Efficiency
  • Reliability/repeatability
  • Health and Safety
  • Infeasible

 

Backdrop

  • Competing against low cost countries
  • Increased wage expectation
  • Reduced funds available
  • Desire for greater profits
  • Tasks unsafe
  • Impossible to do any other way

6

Q image thumb

7

What are the two approaches for the effective control of machining operations

Two approaches for the effective control of machining operations

 

  • Better machine design (Bill)
  • Design of effective control systems

 

NOT MUTUALLY EXCLUSIVE

A image thumb
8

What are the different needs for control systems

Need for control systems

  • Not all deflections in a machine can be dealt with in design
  • Static deflections
    • Unknown & varying workpiece size, shapes
    • Different loading positions
  • Dynamic deflections/vibrations
    • Dependent on different material/tool combinations can’t allow for all of them
    • Different external vibration sources
  • Thermal deflections
    • Unknown heat sources
    • Difficult to predict heat paths & thermal responses exactly

9

What are the different types of control and their characteristics

Proportional control

  • Quick response
  • Disturbance rejection
  • Always steady state error
  • Might cause stability problems

 

Proportional integral control

  • As above +
    • Zero steady-state error
    • Might cause stability problems and oscillations

 

Proportional integral derivative control

  • As above +
    • Improved stability
    • Increased damping
    • Sensitive to noise

10

What are the costs and benefits of closed loop systems?

Benefits of C/L

  • Accuracy
  • Respond to changes
  • Reject disruptions
  • Less precision required in actuation

Costs of C/L

  • Additional sensors
  • More complex control
  • More maintenance
  • Potentially unstable

11

What is adaptive control?

Adaptive machine control

 

  • For expensive machines additional control requirements are sometimes employed
  • Advanced control for machining is defined as the on-line adjustment of process parameters for the purpose of:
    • Optimising production rate (using feed rate)
    • Optimising quality (force, speed)
    • Minimising cost of materials and components (force, speed)
    • Protecting machine (force, torque, power)

A image thumb
12

What are the two types of adaptive control?

Two types of adaptive control

  • Adaptive control constrained (ACC)
    • Places a constraint on a process variable
    • E.g. if the thrust force and cutting force is excessive, the AC system will change the cutting speed to lower the cutting force
  • Adaptive control optimised (ACO)
    • Systems that optimise an operation
    • E.g. maximising removal rate
    • More complex to implement

13

What are the different sensing issues?

Sensing issues

  • Cost
  • Accuracy
  • Timeliness
  • Repeatability
  • Reliability
  • Maintainability

 

Need to consider the number, type and location of sensors. The cost of purchase, installing and maintaining sensors has to be balanced by improved performance.

A image thumb
14

Difference between direct sensing and indirect sensing?

Direct

  • Accurate
  • Complex to install, maintain and expensive

 

Indirect

  • Simpler to maintain and cheaper
  • Less accurate

A image thumb
15

What is the difference between NC and CNC?

Numerical control – method for controlling the movements and support operations of machining components via the insertion of coded instructions (typically numerical) from a computer or other mechanism

 

Computer numerical control – integrates computer-based instructions into NC machines. Either via remote programming or integration of a computer/microprocessor as an integral part of the machining unit

A image thumb
16

What does an NC prgramme comprise?

An N.C. programme comprises

 

  • Header (preparatory) – cancels pre-existing settings, sets data types, data units, tool prep, turns on coolant
  • Body (main tasks) – moves tool into place, performs tasks, moves tool to safe place
  • End (completion) – stop tool, terminate program

A image thumb
17

What are the two categories of offsets in a machine tool?

Tool and workpiece datum/ reference points considerations

  • Offsets are used to redefine the workpiece relative to the datum points in manufacture of machine tool
  • Two categories of offset
    • Zero offsets define the workpiece datum relative to machine
    • Tool offsets which define the tool cutting point relative to the tool reference point

18

What are the different categories of tool offset compensations?

  • Tool length compensation – allows programmer to program all tools as if they are of equal length
  • Tool nose radius compensation – used in turning machines

Cutter radius compensation – causes the controller to alter the programmed path to allow for differences between actual and programmed cutter

19

What is a manufacturing robot?

What is a manufacturing robot:

 

A re-programmable device designed to both manipulate and transport parts, tools or specialised manufacturing implements through variable programmed motions for the performance of specific manufacturing tasks

A image thumb
20

What are the different robot types and DOFs

Robot types and DOFs

 

Anthropomorphic: 6 DOFs

Delta: 6 DOFs

SCARA: 4 DOFs

Cartesian: 3 DOFs

A image thumb
21

What are the different robot performance measures?

Robot performance measures

  • Operation selection
    • Working volume
    • Payload
    • Speed
  • Operation performance
    • Resolution
    • Accuracy
    • Repeatability
    • Safety

22

Compare the different robot types

 

Cartesian: Big reach, low speed, high-ish payload, high repeatability

Anthropomorphic: High reach, average speed, high payload, low repeatability

Scara: high speed, average reach, high repeatability, low payload

Delta: high speed, low reach, low repeatability, low payload

A image thumb
23

What are the three basic methods for programming robots?

  • Teach mode
  • Lead through
  • Off-line

24

What are the pros and cons of the different programming methods?

Teach mode

Pros

  • Simple widely used technique
  • No additional infrastructure required during programming

Cons

  • Time consuming and repetitive
  • Limited automated testing and verification

 

Lead through

Pros

  • Mimics complex trajectories used by skilled operators

Cons

  • Difficult to deal with large robots
  • Inaccuracy’s in programming can’t be edited

 

Off-line

Pros

  • Reduced down time during in programming
  • Assists cell design and allows process optimisation

Cons

  • Requirement for accurate CAD models of instillation
  • Accuracy of robot is critical when suing off-line programming techniques

A image thumb
25

What are the requirements in cell automation?

Cell automation requirements

  • Receive and interpret part schedules
  • Ensure the production of one or more parts is completed
  • Communicate part completion reports to factory computer network
  • Coordinate the functions of different automated machines
  • Distribute operational commands to machines/devices
  • Receive status/completion reports from machines/devices

A image thumb
26

What is PLC?

PLC

  • PLC programming provides a software environment for building sequences of logical operations.
  • A PLC has a microprocessor and memory and a user interface. It is also able to connect to the network to connect to other machines

 

 

27

Describe the approach to ladder logic programming

Approach to ladder logic programming

 

  1. Determine key processing steps
  2. Determine resources/equipment required
  3. For each resource specify:
    1. Triggers (control inputs)
    2. Operations
    3. Pre-requisites
    4. Constraints
  4. Identify allowable states for each resource
  5. Using key processing steps (1) and allowable state (5)
    1. Identify single or joint states required for the process
    2. Develop state model for required operations
  6. For each process state identify
    1. Required inputs from equipment
    2. Required output signals to equipment
    3. Any latching, counting, timer requirements
  7. Generate equivalent ladder code to represent each state

28

What are the different PLC programming approaches

PLC programming approaches

  • Ladder logic
  • Function block
  • Sequential function charts
  • Structured text
  • Instruction set

29

What is function blocks?

FUNCTION BLOCKS

  • Further graphical approach to representing PLC logic
  • Allows for more complex functions to be developed in PLC environment

A image thumb
30

What are sequential function charts?

SEQUENTIAL FUNCTION CHARTS

  • Graphical environment for PLC code development
  • Flowchart approach to logic representation
  • Allows for nesting of logic code
  • Uses 3 logical elements
    • STEP
    • TRANSITION
    • FLOW LINE
  • Can generate equivalent ladder code

A image thumb
31

What is structured text

STRUCTURED TEXT

  • More formalised text based programming language
  • Recognising that PLCs now have full computer capabilities
  • Low level programming language similar to assembler

A image thumb
32

What are the arguments for PC and PLCs for cell automation?

PC vs PLC for Cell automation

 

PC

  • Graphical user interfaces
  • Easy and open networking
  • Excellent computational/memory facilities
  • Relative low initial cost (for multiple applications)

 

PLC

  • Operating systems designed for multi tasking capabilities
  • Robustness of input/output handling
  • Reliability
  • Easy problem diagnosis/recovery

33

What are the informal approaches to logic?

Approaches to logic (informal)

 

  • IMMEDIATE: can execute a solution immediately
  • INSPECTION: solution can be determined after examining the problem
  • STRUCTURE INSPECTION: solution can be determined after following a set of checks
  • PLANNING PROCEDURE: a formal set of steps is used to determine the approach to solving the problem
  • ALGORITHM: An algorithm is executed which generates a solution to the logic problem

34

What are the limitations of State Modelling

 

  • Capture of STATE information can be cumbersome
  • No explicit method for representing transition conditions between states

 

No formal way to express complex logic

  • Conflict between operations requiring
  • Representation of causality
  • Ensuring events occur concurrently

 

Lack of analysis tools for assessing

  • Feasibility of sequence of operations (e.g. avoiding deadlocks)
  • Boundedness of buffers
  • Reachability of required conditions
  • Potential for process simplification

35

What is a petri net?

Petri Nets

 

Graphical tool which can be used for modelling, planning, control design and evaluation of manufacturing systems.

A petri net is a discrete event model which models the change of conditions before and after an event, and the factors required for that event to occur.

36

Explain causality

CAUSALITY: sequential firing of transitions via synchonisation

A image thumb
37

What is deadlock?

 

What is deadlock: when a system can’t get out of itself

A image thumb
38

What is the approach to petri net modelling?

An Approach to Petri Net Modelling

 

  1. Determine key processing steps/states
  2. Determine resources/equipment required
  3. For each resource specify:     
    1. Triggers (control inputs)
    2. Operations
    3. Pre-requisites
    4. Constraints
  4. Develop PN model to reflect key processing steps
  5. Introduce materials handling steps into PN from 4
  6. Identify allowable states for each resource and develop a PN for that resource
  7. Check each PN in 5, 6 to ensure causality, conflict and concurrency conditions and that any upper bounds on capacity are reflected
  8. Combine PNs from 5, 6 to form an overall system PN.

 

39

What is handshaking?

Confirmation / Handshaking

Most machines are equipped with an operational signal which can be incorporated as a confirmation flag for the cell controller (typically a PLC).

This introduces an additional state into the controller operation but greatly enhances reliability and diagnostic capability.

The process is called handshaking

A image thumb
40

What is the multi level view of the factory?

 

Multi level view of the factory

 

TASK: machine, robot, conveyor

 

PART: machining centre, cell

 

PRODUCT: production line, flexible manufacturing systems, storage

 

ORDER: factory

A image thumb
41

Explain the factory decision and control levels

 

LEVEL 0: the physical production process

MANUFACTURING CONTROL

LEVEL 1: sensing the production process, manipulating the process

LEVEL 2: monitoring, supervisory control and automated control of the production process

MANUFACTURING OPERATIONS MGMT.

LEVEL 3: work flow to produce desired products. Maintaining records and optimising the production process

BUSINESS PLANNING AND LOGISTICS

LEVEL 4: Establishing the basic plant schedule – production, material use, delivery etc.

A image thumb
42

Explain the difference between deterministic and non deterministic systems

Deterministic (traffic lights)

  • Guaranteed flow
  • Predictable
  • Inefficient
  • Always a chance of stopping
  • Good for: heavy traffic (individual)

 

Non – deterministic (roundabout)

  • Not guaranteed – potential bottlenecks
  • Maximum use made of the intersection
  • Only stop in heavy, constant traffic
  • Good for light traffic, heavy traffic (total flow)

A image thumb
43

What is MMS?

Manufacturing messaging specification

  • MMS specifies the message exchange between programmable devices for computer integrated manufacturing
  • MMS is a service element in ISO – the application layer
  • Adherence to MMS exchanges increases the flexibility and interchangeability of different manufacturing units

A image thumb
44

What are the different forms of communications in a factory and give examples.

 

Machine communications: MMS

Intra Cell communications: field bus

Between Cell communications: RFID

Factory Wide communications: Ethernet

A image thumb
45

What are part handling systems?

Part Handling Systems

 

  • Material integration between cells, between machining centres and other processing operations
  • Vary in degrees of flexibility
    • Predetermined routing and sequences
    • Predetermined routing variable sequences
    • Free movement in all directions
  • Selection Criteria
    • Material
    • Tasks – variety of them
    • Workpiece loads
    • Workplace size and environment
    • Cost

46

What are part storage systems?

Part Storage Systems

 

  • Part storage between cells, between machining centres and other processing operations to enable batch/ semi batch operations
  • Vary in degrees of flexibility & control
    • FIFO buffers / accumulation buffers
    • Sorting buffers
    • Random access buffers
  • Selection criteria
    • Location: in situ vs storage
    • Size: part size, volumes (control strategy)
    • Manual vs automated access

47

Explain the progression of digital manufacturing

 

Digital manufacturing

 

1990s (agility, globalisation)

  • The application of digital information for the enhancement of manufacturing processes

2000s (energy, emissions, sc integration)

  • The application of digital information for the enhancement of manufacturing processes, supply chains

Late 2010s (distributed, small scale production, customisation, e commerce)

  • The application of digital info (from multiple sources) for the enhancement of manufacturing processes, value chains, products and services

48

Whats new whats not? (internet manufacturing)

Whats new?

  • Internet is ubiquitous
  • Network many devices/ objects/ data sources
  • Cloud computing
  • Mobile, personal computing
  • IT services
  • Ability to share information across value chain
  • Order information orientation
  • Customer involvement

 

Not new

  • Lots of sensors
  • Lots of data
  • Data analytics
  • Simulation
  • Industrial AI

49

What is industry 4.0

 


A framework for enabling the integration of physical and digital resources, services and humans resources in manufacturing in real time

 

  • Vertical integration and networked manufacturing systems
  • Horizontal integration through value networks
  • End to end digital integration of engineering across the entire value chain
  • With real time optimisation

A image thumb
50

What are the main developments at the moment?

Industry 4.0

Internet of things

Cyber physical systems (digital twin)

Block chain

Augmented reality