Navigation

  • Page 1

    Discrete Control Logic 1. Pneumatic circuits - Low forces - Discrete, fixed travel distances - Rotational or reciprocating motion Main components: compressor, valves, cylinders

  • Page 2

    •double -actingspring-returnair supplyvent to atmosphere (air discharge)Pneumatic components: cylinders tepping away from this mat, the person has to manually switch the robot back ON

  • Page 3

    Pneumatic components: valves a 3/2 valvea 5/2 valvereturn springpneum aticpush buttonfoot pedalsolenoid (electrical)roller (m echanical)valve actuation

  • Page 4

    ••Start•VAA+A-A-+Simple Pneumatic control START, A+, A-

  • Page 5

    Pure Pneumatic control design: Cascade method Example: Punch Press Operation: (i) part is clamped in position (ii) press punches the part (iii) the clamp is released (iv) part is removed from the table START, A+, B+, B-, A-, C+, C- Functions of A, B, C ? How to design pneumatic system?

  • Page 6

    Pure Pneumatic control design: Cascade method (1) Write cylinder action sequence (2) Partition sequence into minimum no. of groups (no letter repeated in group) (3) Merge last group, first group (if possible) (4) Each cylinder is double-acting (5) Each cylinder is controlled by 5/2 valve (both ...

  • Page 7

    Cascade method: forming groups Break it down into groups: START, A+, B+ / B-, A-, C+ / C- GRP 1 GRP 2 GRP 3 START, A+, B+, B-, A-, C+, C- Merge Group 3 with Group 1 ? START, A+, B+ / B-, A-, C+ / C- GRP 1 GRP 2 GRP 1

  • Page 8

    Cascade method: draw cylinders, manifolds, valves - Draw the cylinders - For each cylinder, draw the limit valve (3/2 way) - For each cylinder, draw the control valve - Draw manifold lines - Limit valve connections: a2, b2 and c1 get their air supply from manifold 1 a1, b1 and c2 get thei...

  • Page 9

    Cascade method: forming groups Start-+-+-+••••Aa1a2Bb1b2Cc1c2-+VC+-VB-+VA1221Casca de circuit for: START, A+, B+, B-, A-, C+, C-

  • Page 10

    Pure Pneumatic Controls - For more complex logic, difficult to debug - Less versatile than electronic control (e.g. no counters, poor timer control) - pneumatics timer control: delay valves.

  • Page 11

    Programmable Logic Controllers History: avoiding complex/large relay boards - Why are relay boards required? PLC Basics: computer + relays A/C 220Vinput 0input 1input 2input 3input 4input 5input 6Power supply wireO u t p u t sBox with Computer (controller)data communication wire

  • Page 12

    PLC: example 1 Pressure_Switch is ON Warning_Light ON

  • Page 13

    PLC: example 1 STEP 1: Write this logic into a PROGRAM STEP 2: Load program into PLC STEP 3: Connect the sensor output to External Input terminal. STEP 4: Connect the PLC External Output Terminal to Warning Light STEP 5: EXECUTE the logic program on the PLC.

  • Page 14

    PLC: example 1 Programming language: LADDER LOGIC

  • Page 15

    PLC: example 1 Programming language: LADDER LOGIC IF THEN

  • Page 16

    PLC: example 2 Outer mat ON  warning light ON Inner mat ON  warning light ON AND Robot OFF Stepping away from inner mat  Manually switch robot ON

  • Page 17

    PLC: example 2 Two actuators: Warning light, Robot master switch LOGIC for Warning light External Input 1: outer mat External Input 2: inner mat External output: light

  • Page 18

    PLC: example 2 LOGIC for Robot LOGIC for Warning Light PROBLEM ?

  • Page 19

    PLC: example 2 LOGIC for Robot Robot must STAY OFF until manual reset to ON Solution: LATCH External Input 2: inner mat Internal (logical) relay latch External output: robot

  • Page 20

    PLC: example 2 LOGIC for Robot Robot must STAY OFF until manual reset to ON

  • Page 21

    Ladder Logic Programs Switch (Relay) naming conventions Lecture notes (Rockwell™ Automation PLC): External inputs: I:0/1, I:0/2, …, I:1/1, I:1/2, … I:n/m External outputs: O:0/1, O:0/2, …, O:1/1, O:1/2, … O:n/m Internal Relays: B0, B1, … etc. Lab (SMC™ PLC): External inputs: X0,...

  • Page 22

    PLC Example: XOR Logic A xor B: (A is ON AND B is OFF) OR (A is OFF AND B is ON)

  • Page 23

    Ladder Logic: Timers Solenoid actuated door-lock Solenoid ON for 5 sec, then OFF Solenoid ON  Door unlocked Solenoid actuated when: (i) ON signal from number-pad outside door (ii) ON signal from door-open switch inside door While O:0/1 remains ON, Timer COUNTS DOWN from PRESET COUNT D...

  • Page 24

    Ladder Logic: Timers Solenoid actuated door-lock Solenoid ON for 5 sec, then OFF Solenoid ON  Door unlocked Solenoid actuated when: (i) ON signal from number-pad outside door (ii) ON signal from door-open switch inside door

  • Page 25

    Ladder Logic: Timers -- reset Solenoid ON for 5 sec, then OFF Solenoid actuated when: (i) ON signal from number pad outside door (ii) ON signal from door-open switch inside door During ON, if button is pressed, Timer resets to PRESET During ON, light indicator is ON LEGEND: I:0/1  door-...

  • Page 26

    Ladder Logic: counters Count the number of occurrences of an event Pallet loading in factory After 10 parts arrive on conveyor, worker comes to load pallet Examples: Pneumatic press hammer Hit the part 20 times, then wait for part to be unloaded Rice cooker alarm Beep 5 times when rice is cook...

  • Page 27

    Ladder Logic: counters Pallet loading in factory After 4 parts arrive on conveyor: STOP conveyor belt turn ON the indicator light

  • Page 28

    Ladder Logic: car wash Car arrives  limit switch ON Limit switch ON  Washer ON Washer ON: (i) Soapy water SPRAY ON (30 secs) (ii) Rinse: clean water SPRAY ON (30 secs) (iii) Automatic scrubber brushes car (15 secs) (iv) After washing 50 cars, the scrubber brush Auto-change

  • Page 29

    I:0/1I:0/2B1O:0/0B1T4 :0T4 :1T4 :2O:0/1B1O:0/2B1O:0/3B1B1B1I:0/1 : System On I:0/2 : Em ergency Stop I:0/3 : Lim it SwitchO:0/0 : Soa p Wat er On O:0/1 : Rinse On O:0/2 : Sc rubber On O:0/3 : Ac tiva te Scrubbe r ChangeNotice how B1 and the time r outputs are used to c ontrol the logic ac cordin...

  • Page 30

    Programming a PLC (1) Hand held console (direct feed of program into PLC) (2) Computer-interface: (i) Complete the program on a computer (ii) Test the program on PC (iii) Upload the program to the PLC processor memory (persistent) (iv) Connect external Inputs and Outputs (v) Run the program ...

  • Page 31

    Operation cycle of PLC Phase 1Phase 2Phase 3Program MemoryProcessorAccumulatoroutput registeroutput30373031323334353637inputinput register0001020304050607080910110011

x