the cascade method - national university of singaporeguppy.mpe.nus.edu.sg/anpoo/ia/cascade...

1IA IA –– Cascade MethodCascade Method

The CASCADE MethodThe CASCADE Method

• similar to that for electromechanical devices. • involves dividing the sequence into groups

with each group’s manifold (power or main pressure line) being supplied with pneumatic power (pressure) one at a time and in sequence.

• Motion within each group is powered by its own group manifold.


The CASCADE Method The CASCADE Method –– Step 1Step 1

Divide the sequence into Groups so that no letter is repeated within any Group.

Example:

START, A+, B+, B-, A-, C+, C-I II I



Step 2: For each cylinder, assign a 4/2(or 5/2) control valve with double pilot lines (i.e., without spring return) and two spring-return 3/2 limit valves to indicate end of strokes.

Step 2: For each cylinder, assign a 4/2(or 5/2) control valve with double pilot lines (i.e., without spring return) and two spring-return 3/2 limit valves to indicate end of strokes.

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A

+ -

B

+ -

C

+ -


Step 3: Assign one or more Group Valves or Cascade Valves to control air pressure to the Group manifold lines so that only one Group manifold line is pressurised at any one time and in sequence.


1 2

I II

1 3

2

IIIIII

1

3

2

4

IIIIIIIVExamples of Cascade Valves for 2, 3 and 4 groups. I, II, III and IV are outputs to Manifolds. 1,2,3 and 4 are input control lines to switch to their respective groups.

Examples of Cascade Valves for 2, 3 and 4 groups. I, II, III and IV are outputs to Manifolds. 1,2,3 and 4 are input control lines to switch to their respective groups.

III


START, A+ B+ B- A- C+ C-I II I



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B

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C

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1 2

I

II


Step 4 There are two approaches.Approach 1: Design according to the sequence and using your understanding of how the Cascade Method is intended to work. The principal basis is the switching of the Group manifolds.

Approach 2: Design according to a set of rules worked out according to the principles of the Cascade Method.

Step 4 There are two approaches.Approach 1: Design according to the sequence and using your understanding of how the Cascade Method is intended to work. The principal basis is the switching of the Group manifolds.

Approach 2: Design according to a set of rules worked out according to the principles of the Cascade Method.


A

+ -

B

+ -

C

+ -

1 2

I

IISTART

a- b- c- c+b+a+

START A+ B+ B- A- C+ C-I II I

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Approach 1Approach 1• Begin with START. Input to START comes from c- limit

valve and output goes to initiate A+ motion.

• After A+ motion, take input to a+ from its own Group Imanifold and output to initiate B+ motion.

• Begin with START. Input to START comes from c- limit valve and output goes to initiate A+ motion.

• After A+ motion, take input to a+ from its own Group Imanifold and output to initiate B+ motion.


A

+ -

B

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C

+ -

1 2

I

IISTART

a- b- c- c+b+a+


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Approach 1Approach 1• At the end of the B+ motion, limit valve b+ is actuated.

Connect its input to its own Group I manifold and take the output signal to switch to Group II.

• At the end of the B+ motion, limit valve b+ is actuated. Connect its input to its own Group I manifold and take the output signal to switch to Group II.


A

+ -

B

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C

+ -

1 2

I

IISTART

a- b- c- c+b+a+


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Approach 1Approach 1• We’re in Group II now. First action is B-. Connect Group II

manifold to initiate B- motion.

• At the end of B- stroke, connect input of b- to its own Group II and output to initiate A- motion.

• We’re in Group II now. First action is B-. Connect Group II manifold to initiate B- motion.

• At the end of B- stroke, connect input of b- to its own Group II and output to initiate A- motion.


A

+ -

B

+ -

C

+ -

1 2

I

IISTART

a- b- c- c+b+a+


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Approach 1Approach 1• At end of A- stroke, a- limit valve is actuated. It then take

Group II power, connected to its input, and its output initiates C+ motion.

• At end of C+ stroke, need to use c+ to switch to Group I.

• At end of A- stroke, a- limit valve is actuated. It then take Group II power, connected to its input, and its output initiates C+ motion.

• At end of C+ stroke, need to use c+ to switch to Group I.


A

+ -

B

+ -

C

+ -

1 2

I

IISTART

a- b- c- c+b+a+


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Approach 1Approach 1• We’re now into Group I. First action is C-. Thus, connect

Group I manifold to initiate C- motion.

• At end of C- stroke, c- takes its input from Group I and output its signal to the next action, which is START. ☺

• We’re now into Group I. First action is C-. Thus, connect Group I manifold to initiate C- motion.

• At end of C- stroke, c- takes its input from Group I and output its signal to the next action, which is START. ☺


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B

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C

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1 2

I

II


Step 4 Connect the input of the limit valve at each stroke extremity to its own Group manifold…Step 4 Connect the input of the limit valve at each stroke extremity to its own Group manifold…

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Approach 2Approach 2



Step 5 For the first letter in each Group, connect the corresponding control valve input to its own Group manifold …Step 5 For the first letter in each Group, connect the corresponding control valve input to its own Group manifold …

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B

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C

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I

II



Step 6 For the last letter in each Group, connect the output of the corresponding limit valve to switch to the next Group …Step 6 For the last letter in each Group, connect the output of the corresponding limit valve to switch to the next Group …

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Step 7 For all other letters, connect the output of the corresponding limit valve to the control valve input corresponding to the next letter in the sequence

Step 7 For all other letters, connect the output of the corresponding limit valve to the control valve input corresponding to the next letter in the sequence

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Step 8 Incorporate a 3/2 spring-returned manually-operated START valve. The circuit should now be completeStep 8 Incorporate a 3/2 spring-returned manually-operated START valve. The circuit should now be complete

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A

+ -

B

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C

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1 2

I

IISTART


Taking care of Repeated MotionsTaking care of Repeated MotionsTaking care of Repeated Motions

START, A+, A-, A+, A-

Cylinders requiring repeated motions will need "OR" logic at the control valve.


START, A+, A-, A+, A-

For each motion, there needs to be an associated limit valve to detect end of motion.

Taking care of Repeated MotionsTaking care of Repeated MotionsTaking care of Repeated Motions


Another example:Another example:Another example:

START, A+, A-, A+, A-IV I II III IV

Because of repeated motion, more than one limit valves are required for each stroke extremities, one for each motion. The bottom figure is an alternative. Shuttle valves are used for the OR logic function.

a+

a1+ a2+



Assign the Cascade Valves for 4 groups making sure that the connections are drawn such that Group 4 Manifold is pressurized since START is in Group 4. Draw in the four Group Manifold lines.




For the first letters in each group, connect the relevant input of the cylinder control valve to its own group manifold. For this example, all the four letters are first letters.




According to Step 4, connect all the inputs of all limit valves to their own group manifold lines. Connect the input of the START push-button to the output of the previous action, in this case, the output of limit valve corresponding to the 2nd A-motion.




The two A+s, the first A-, and START are all last actions in their respective groups. Connect the outputs of the corresponding limit valves, and of START, to switch to the next group. In the case of START, this is to switch to Group I. The circuit now should be complete.



End of Cascade MethodEnd of Cascade Method

the cascade method - national university of singaporeguppy.mpe.nus.edu.sg/anpoo/ia/cascade...

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