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    ME3242/ME3242E NATIONAL UNIVERSITY OF SINGAPORE ME3242/ME3242E – INDUSTRIAL AUTOMATION (Semester I : AY2010/2011) Time Allowed : 2 Hours INSTRUCTIONS TO CANDIDATES: 1. This examination paper contains FOUR  ( 4 ) questions and comprises FIVE  ( 5 )  printed pages. 2. Answer ALL FOUR (4)  questions. 3.   All questions carry equal marks. 4. This is a CLOSED-BOOK EXAMINATION with authorized materials:  One A4-sheet of note/formulae written/printed on both sides is allowed into the examination room.  Page 2 ME3242/ME3242E QUESTION 1 (a) Figure 1.1 shows a spool-based 3/2 directional valve. Express the Boolean relationship of the output T   in terms of the inputs 1  x  , 2  x  and 3  x  . (5 marks) x 1 x 2  x 3 T   Figure 1.1 (b) Figure 1.2 shows four pneumatic push buttons  A ,  B , C   and  D. Design a pneumatic circuit to express the Boolean expression  D B AC  B A D B AC  B AY   ⋅⋅+⋅⋅+⋅⋅+⋅⋅=  using the minimum number of valves. (7 marks)  A B C D   Figure 1.2 (c) In an automation process, four pneumatic cylinders  A ,  B , C   and  D  are used to perform a specified sequence of A+ B+ A- D+ C+ A+ D- B- A- C-. Each of the cylinder is controlled by a 4/2 valve with double pilot activation. Design a fully pneumatic circuit such that when a START button is briefly pressed, it activates the above sequence of actions. (13 marks) Continue on next page….  Page 3 ME3242/ME3242E QUESTION 2 Figure 2.1 shows the desired sequence for an automation task which involves five cylinders,  A ,  B , C,    D  and  E  . Each cylinder is controlled by a 4/2 valve with double solenoid activation and two SPDT limit switches for the detection of the fully extended and fully retracted  positions of the cylinder.  A+ B+C+D+ A-D-E+ E-B- C-   Figure 2.1  (a) Design a ladder circuit such that when a START button is briefly pressed, it activates the above sequence of actions. (15 marks) (b) The automation of the above sequence is to be implemented using a PLC. Choose appropriate PLC inputs and outputs for your input/output devices and write the corresponding PLC program in Instruction List.  (10 marks ) Continue on next page…    Page 4 ME3242/ME3242E QUESTION 3 Figure 3.1 shows two pneumatic cylinders A and B that are used for an automation process. Each cylinder is controlled by a single solenoid and spring return 4/2 valve. Each cylinder is also fitted with two limit switches to detect its fully retracted and fully extended positions as shown in Figure 3.1. The ladder logic to control these cylinders is shown in Figure 3.2. Using a sequence chart to trace the state of these components when the START button is  briefly pressed. What is the sequence of actions when the START button is briefly pressed? (25 marks) b 1  b 2 Ba 1  a 2  A  A+B+   Starta 1   Y 1 Y 2 y 1 y 2 a 1 y 1  y 2  b 2 y 2 y 1 b 1 Vcc y 1  y 2  A+ y 1  y 2 B+ y 1  y 2  a 2 y 1  y 2 y 1  y 2  a 2   Figure 3.1 Figure 3.2 Continue on next page….
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