Automation Operations and Programmable Controllers

Mechatronics Definition

  • Integration of mechanical, electrical, fluid, and computer technologies.
  • Used to control machine movements.
  • Term introduced in the early 1970s by a Japanese firm.
  • Combines mechanics and electronics for decision-making, now often by a computer.

Mechatronics Application

  • Assembly lines using robots and automated devices.
  • Material transported by conveyors.
  • Electrical sensors monitor operation.
  • Programmable controllers manage movements.
  • Systems are networked for communication and process tracking.

Pick-and-Place Automation Systems

  • Picks up parts from one location and places them in another.
  • Controlled by a PLC, using pneumatic or hydraulic valves, or servo-controlled.
  • Used for material handling, machine loading/unloading, and sequential assembly.

Flexible Manufacturing System Definition

  • Automated machines linked by a material handling system and a controller.
  • Programmed to make various products or parts.
  • Advantage: Cost reduction due to:
    • Ability to produce multiple products with one set of equipment.
    • Reduced setup time through reprogramming.
    • Small batch runs and lower inventory costs.

Small Flexible Manufacturing System

  • One or two CNC machining stations loaded by a robot.
  • Centrally controlled by a programmable controller.
  • Robot loads raw material and unloads finished parts.
  • PLC signals the robot and CNC machine to change programs.

Large Flexible Manufacturing System

  • Multiple stations linked by a programmable material handling device (e.g., conveyor).
  • Parts moved from station to station under a central computer (often a PLC).
  • Each station performs a part of the manufacturing process.
  • Stations may have individual PLCs communicating with the central PLC.
  • Used in machining for aerospace and automotive industries, and virtually all types of manufacturing.

Examples of Automated Manufacturing Processes

  • Inventory Storage and Retrieval
  • Material Handling
  • Material Processing
  • Finishing
  • Assembly
  • Inspection

Inventory Storage and Retrieval

  • Automated system (ASRS) provides raw material and stores finished goods.
  • Specialized robot-like devices load and unload parts from warehouse racks.
    • Centralized: All inventory in one central location.
    • Decentralized: Materials fed to the required process at workstations, often by parts feeders or robots.

Material Handling

  • Flexible material handling (FMH) system automatically moves material between workstations.
  • Can be programmed to move material to specific workstations.
    • Programmable Conveyors: Transport material over specific paths. Uses a PLC to move materials to workstations.
    • Synchronous: Indexes parts from station to station with the same path and cycle rate.
    • Asynchronous: Parts move independently.
    • Pallet Transfer Conveyor: A synchronous conveyor that transports parts on pallets.
    • Pallet Advantages: Same dimensions, guided easily, stopped accurately at each station.
    • Automatic Guided Vehicles (AGVs): Unmanned vehicles that transport materials between workstations following a programmed path.
    • Uses: Substitutes for conveyors when distances are large or conveyors obstruct movement.

Material Processing

  • Workstations consist of CNC machines and a robot for loading/unloading.
  • Processes include machining, casting, and molding.
    • Machining: Material removal processes like milling, turning, grinding, laser cutting, water jet cutting, EDM, and routing.

Finishing

  • Improves appearance or provides a protective coating.
  • Examples: Polishing, grinding, trimming, painting, anodizing, and chrome plating.
  • Uses robots to perform finishing tasks.

Assembly

  • Joining two or more separate parts using mechanical fastening, welding, brazing, soldering, or gluing.
  • Automated assembly workstations use robots or PLC-controlled pick-and-place devices.

Inspection

  • Determines if the part or product meets design specifications through measurement, vision inspection, or functional testing.
  • Inspection workstations use specialized machines or devices directly on the material handling system.

Basic Sequencing Control Systems Model

  • Controller programmed to make machine components perform a series of actions (machine sequence).
  • Controller connected to input and output devices.
  • Logic turns outputs on/off based on input signals.
  • Each step starts with input signal(s), and logic decides which outputs to activate.

Triggering Input Devices

  • Arranged so the completion of one step triggers the next via an input device.

Clamp and Drill Example

  • A 4-step sequence controlled by a PLC:
    • Step 1: Clamp Cylinder Extend.
    • Step 2: Drill Cylinder Extend.
    • Step 3: Drill Cylinder Retract.
    • Step 4: Clamp Cylinder Retract.

Control Panels

  • Allow operator to control and monitor basic machine functions.
    • Pushbutton Switches: Send manual input signals to the controller.
    • Momentary: Returns to original position when released.
    • Maintained: Stays pushed in until de-actuated.
    • Pushbutton Switch Types:
    • Mushroom Head: For emergency stop.
    • Extended: Easily seen from all angles.
    • Flush: Prevents accidental actuation.
    • Selector Switches: Change the mode of operation (On/Off, Manual/Automatic, etc.).
    • BCD Thumbwheel Switch: Provides multiple inputs to input data, such as time delay or production count.
    • Converts decimal number (0-9) to BCD value.

Output Devices

  • Indicator Lamps: Indicate machine status.
  • Audible Alarms: Alert the operator to events needing immediate attention.
  • Message Displays: Display information about machine or process status.
  • LED Display: Shows values stored in PLC memory (e.g., elapsed time, production level).

Types of On/Off Sensors

  • Used to detect actuator position (automatic input devices).
    • Limit Switches: Sense position mechanically.
    • Magnetic Reed Switches: Close contacts in a magnetic field.
    • Capacitive Proximity Sensors: Sense presence using capacitance.
    • Inductive Proximity Sensors: Sense metallic objects using induction.
    • Photoelectric Proximity Sensors: Energize output when sensing light.
    • Infrared Proximity Sensors: Output infrared light.
    • Fiber Optic Proximity Sensors: Use fiber optic filaments to send and receive light.
    • Hall Effect Sensors: Energize output when a magnetic field is sensed.
    • Giant Magnetoresistive Sensors: Respond to magnetic field orientation.

Output Devices

  • Controllers connected to output devices control power flow to actuators.
    • Directional Control Valves (DCVs): Control motion by directing fluid flow.
    • Motor Starter: Functions as a large relay to start and stop a motor; includes overload protection.

Safe Dress Rules

  • Safety glasses, hearing protection.
  • Avoid loose clothing, jewelry.
  • Tie up long hair.
  • Heavy-duty leather shoes (steel-toed recommended).
  • Roll up or wear short sleeves.
  • No gloves around running machinery.

Safety Rules

  • Stop machine completely before entering operation area.
  • Lockout/tagout all power sources before maintenance.
  • Remove pressure from the system.
  • Secure compressed air hoses.
  • Remove obstructions.
  • Check for damage.
  • Remove robot teach pendants.
  • Locate emergency stop buttons.

Role of a Modern Automated Machine Operator

  • Operate computer-based terminals, performing quality assurance, and basic maintenance.

Typical Operator Panel Functions

  • Push Buttons
  • Selector Switches
  • Indicators
    • Start Pushbutton: Starts the machine cycle.
    • Cycle Stop: Stops the machine at the end of its current sequence.
    • Emergency Stop: Removes power quickly.
    • Manual/Automatic: Selector switch controls mode.
    • Jog: Manually operates actuators.
    • Halt: Pauses the sequence after the current step.
    • Indicator Lamps: Indicate machine status.
    • Red: Danger, abnormal/fault condition.
    • Amber: Attention needed.
    • Green: Safe condition.
    • White/Clear: Normal condition.
    • HMI Operator Panel: Replaces wired control panels, providing input control and output display.

Stop Categories

  • Category 0: Immediately removes power.
  • Category 1: Controlled stop, then removes power.
  • Category 2: Controlled stop, leaves power available.

Steps to Operate an Automated Machine

  • Step 1: Perform Safety Checks
  • Step 2: Prepare Machine for Startup
  • Step 3: Remove Lockout/Tagout Devices
  • Step 4: Power Up the Machine:
  • Step 5: Turn On PLC Output Power
  • Step 6: Home/Reset Actuators and Robots
  • Step 7: Place System in Auto Mode
  • Step 8: Start Operation
  • Step 9: Stopping the Machine (Halt, Cycle Stop, Emergency Stop)
  • Step 10: Shutdown

PLC Definition

  • Programmable Logic Controllers (PLCs) are industrial computers.
  • Control machines and industrial applications.
  • Replace hardwired devices like relay coils and contacts.
  • Examples of Applications: Assembly Machines, Automatic Transfer Lines, Packaging Lines, Robots

PLC Advantages

  • Less Space
  • Lower Cost
  • Resistance to Environment
  • Direct Interface
  • Easy Programming
  • Flexibility

Basic Components of a PLC

  • Input Terminals
  • Output Terminals
  • Processor Module (Controller)
  • Programming Device

PLC Programming Methods

  • Personal Computer
  • Memory Module
  • Handheld Terminal

PLC Scan Cycle

  • Inputs -> Ladder Logic -> Outputs

Three Operational Steps of Scan Cycle:

  • One completion of the three operational steps is called a scan cycle.

Download and Run a PLC Program

  • Interface to the PLC
  • Select Download Option
  • Put the PLC in Run Mode
  • Initiate Program
  • Stop the Program

PLC Programming Languages

  • History: The first PLC (MODICON) used ladder logic.

MicroLogix 1000 Discrete Address

  • I/O Type
  • Slot Number
  • Terminal Number

Input/Output Diagrams

  • Show physical connections between I/O devices and PLC terminals.

PLC Ladder Logic

  • Logic Continuity
  • Six Logic Elements (AND, OR, NOT, NAND, NOR, Memory)
  • Parallel Rung Operation