Circuit building blocks

Transcription

1 Követő vezérlés

2 Circuit building blocks A a0 b0 b1 B Run/End These circuits can be considered as building blocks for larger sequential circuits consisting of two or more cylinders Each actuator will have a power valve and two associated feedback valves. The first actuator to move also has a Run/End valve

3 Repeat pattern sequence A repeat pattern sequence is one where the order of the movements in the first half of the sequence is repeated in the second half Each actuator may have one Out and In stroke only in the sequence There may be any number of actuators in the sequence The signal starting the first movement must pass through the Run/End valve Needs only the basic building blocks to solve Examples of repeat pattern sequences: A+ B+ C+ D+ A- B- C- D- A- B+ C- A+ B- C+ C+ A+ B- C- A- B+

4 Repeat pattern sequence a0 b0 b1 A B Run/End b0 b1 a0 The two cylinders A and B are to perform a simple repeat pattern sequence as follows: A+ B+ A- B- Apply the rule The signal given by the completion of each movement will initiate the next movement In this way the roller valves can be identified and labelled

5 Repeat pattern sequence a0 b0 b1 c0 c1 A B C Run/End c0 c1 a0 b1 b0 For three cylinders A, B and C also to perform a simple repeat pattern sequence as follows: A+ B+ C+ A- B- C- Apply the rule The signal given by the completion of each movement will initiate the next movement

6 Non-repeat pattern sequence a0 b0 b1 A B Run/End a0 b0 b1 If the rule applied to a repeat pattern sequence is applied to any other sequence there will be opposed signals on one or more of the 5/ valves preventing operation This circuit demonstrates the problem The sequence is A+ B+ B- A-

7 Opposed signals a0 b0 b1 A B Run/End a0 b0 b1 When the valve is set to Run, cylinder A will not move because the 5/ valve has an opposed signal, it is still being signalled to hold position by the feedback valve b0 If A was able to move + a similar problem will occur for the 5/ valve of B once it was + The sequence is A+ B+ B- A-

8 Mechanical solution a0 b0 b1 A B Run/End a0 b0 b1 The problem was caused by valves b0 and being operated at the time the new opposing instruction is given If these two valves were one way trip types and over tripped at the last movement of stroke, only a pulse would be obtained instead of a continuous signal

9 Sequence solution methods The main solutions to solving sequences are: Cascade (pneumatic) Shift register (pneumatic) Electro-pneumatic PLC (Programmable logic controller) Cascade circuits provide a standard method of solving any sequence. It uses a minimum of additional logic hardware (one logic valve per group of sequential steps) Shift register circuits are similar to cascade but use one logic valve for every step Electro-pneumatic circuits use solenoid valves and electromechanical relays PLC. The standard solution for medium to complex sequential systems (except where electrical equipment cannot be used)

10 Cascade two group The A+ B+ B- A- circuit is solved by the two group cascade method The sequence is divided at the point where B immediately returns The two parts are allocated groups l and ll Gp l A+ B+ / Gp ll B- A- Two signal supplies are provided from a 5/ valve one is available only in group l the other is available only in group ll Because only one group output is available at a time it is not possible to have opposed signals A standard 5/ double pressure operated valve is the cascade valve Select l Group l Group ll Select ll

11 Cascade (two group) a0 b0 b1 A B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

12 Cascade (two group) a0 b0 b1 A B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

13 Cascade (two group) a0 b0 b1 A B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

14 Cascade (two group) a0 b0 b1 A B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

15 Cascade (two group) A a0 b0 b1 B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

16 Cascade (two group) A a0 b0 b1 B b0 Gp l Gp ll Run/End Sequence Gp l A+ B+ Gp ll B- A- a0 b1

17 Cascade building blocks A two group building block consists of a lever valve to run and end the sequence plus the 5/ double pilot operated cascade valve For a two group system consisting of any number of cylinders this building block and the cylinder building blocks are all that is required to solve the sequence Run/End 1 Sel l Gp l Gp ll Sel ll

18 Cascade building blocks This three group building block establishes an interconnecting pattern that can be extended to any number of groups Run/End Sel l Sel ll Gp l Gp ll Gp lll Sel lll

19 Dual trip building blocks When a sequence has a cylinder operating twice in one overall sequence a dual trip building block may be required for each of the two feedback valves The supply will be from different groups and the output go to different destinations Example is for feedback valve of cylinder A when A is sent + both in Group x and Group y A+ in Group x A+ in Group y Note: can often be rationalised to less than these three components Send A+ in x in y

20 Cascade rules Establish the correct sequence Divide the sequence in to groups. Always start a sequence with the Run/End valve selecting group l e.g. R/E A+ B+ B- C+ C- A- Select the cylinder building blocks Select the cascade building block Select dual trip building blocks if required Interconnect the blocks as follows: The first function in each group is signalled directly by that group supply The last trip valve operated in each group is supplied with main supply air and selects the next group The remaining trip valves are supplied with air from their respective groups and initiate the next function The run/end valve will control the signal from the last trip valve to be operated

21 Pre-select The lever valve can preselect the movement of the cylinder OUT or IN The movement will occur the next time the plunger valve is operated The plunger valve can be released immediately and subsequently operated and released any number of times OUT/IN pre-select

22 5/ OR function The valve at position a is reversed connected and supplied from the valve conventionally connected at position b a The cylinder can be controlled from either position a OR position b b

23 Single pulse control Each time the foot operated valve is pressed the cylinder will single stroke + and - alternately First foot operation the cylinder moves out Second foot operation the cylinder moves in Third.. out and so on

24 Air conservation Power stroke in the instroke direction only Differential area of the piston gives an outstroke force when the pressure is balanced Air used to outstroke is equivalent to a cylinder with only the same bore as the rod diameter Assumes the cylinder is not loaded on the plus stroke and low friction

25 Air conservation Power stroke in the instroke direction only Differential area of the piston gives an outstroke force when the pressure is balanced Air used to outstroke is equivalent to a cylinder with only the same bore as the rod diameter Assumes the cylinder is not loaded on the plus stroke and low friction

26 Double flow Where a larger 3/ valve is not available Two flow paths in a 5/ valve each with a separate supply can be arranged to give double flow or supply separate devices Ensure the tube size to the cylinder is large enough to take the double flow

27 Double flow Where a larger 3/ valve is not available Two flow paths in a 5/ valve each with a separate supply can be arranged to give double flow or supply separate devices Ensure the tube size to the cylinder is large enough to take the double flow

28 Counting Counting applications are best achieved with electro-mechanical or programmable electronic counters Pneumatic counting circuits use large numbers of logic valves and can be slow The counting chain shown will count to 4 Red and blue are nonoverlapping alternate pulses, purple is the reset line 4 3 1

29 Counting application The counting circuit is applied to count 4 strokes of a cylinder A a0 At rest all counting valves are held reset by the start valve Start outstrokes A Alternate signals from and a0 progresses operation of the counting valves up the chain Start On the 4th operation of the green signal resets the start valve to stop the cylinder a0

30 Time delay A signal is restricted to slow the rate of pressure build up on a pressure switch (3/ differential pressure operated valve) When the pressure switch operates a strong unrestricted output is given A reservoir provides capacitance to allow less fine and sensitive settings on the flow regulator making it easy to adjust Signal in Output

31 Time delay Manual remote start of a double acting cylinder with a time delay in the outstroked position before automatic return - + A

32 Pressure decay Manual remote start of a double acting cylinder Uses a low pressure operated valve connected normally open When the back pressure in the front of the cylinder falls below 0.1 bar the return signal is given Connection taken between the cylinder and flow regulator Useful for pressing work pieces of variable size - + A bar

33 Electro-pneumatic The majority of systems use electrical/electronic control due to the high degree of sophistication and flexibility Solenoid valves are used to control cylinders Feedback signals are from reed switches, sensors and electrical limit switches Logic is hard wired or programmed in to a PLC (programmable logic controller) Circuit building block for each cylinder a0 A a