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GCE MAY 2007 : (A2 3) Systems and Control in Product Design- Revised

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ADVANCED General Certificate of Education 2006 Technology and Design assessing Unit 6 Systems and Control in Product Design A2V31 A2V31 Assessment Unit A2 3 [A2V31] WEDNESDAY 31 MAY, MORNING TIME 2 hours 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number on the Answer Booklet provided and on the A3 pro forma answer pages provided. Answer three questions. Answer the one question in Section A and either the two questions in Section B or the two questions in Section C. Answers to Questions 1(a)(v) or 1(b)(v) and 5(c)(ii) should be made on the A3 pro forma answer pages provided. INFORMATION FOR CANDIDATES The total mark for this paper is 80, including a maximum of 4 marks for quality of written communication. Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. At the conclusion of the examination, attach the A3 pro forma answer pages securely to the Answer Booklet with the treasury tag supplied. You are provided with an insert sheet for Questions 1(a) or 1(b). Do not write your answers on this insert. A materials data sheet is provided. A2V3S6 1629 Section A This question is compulsory. You are advised to spend 1 hour and 15 minutes on this section. You are required to answer either 1(a) or 1(b). For candidates studying Electronic and Microelectronic control systems answer part (a) using the pro forma (answer 1(a)(v)) and an answer booklet. 1 (a) The insert Fig. 1(a) shows the latter stage of a prototype packaging line where a batch of crisp boxes, stacked on a pallet, are to be wrapped with cling film. After the pallet is set on the table by a forklift truck the operator takes the end of the cling film and then secures it to a crisp box before closing the safety screen. The wrapping sequence begins with motor/gearbox A rotating the table at a fixed speed and then motor/gearbox B slowly moving the housing up the column. On reaching the top of the column motor/gearbox B then slowly moves the housing down. When the housing is half way down the column an arm, containing a heated element, rotates through 60 degrees to cut the cling film, and then returns to its initial position. The sequence ends once the housing is returned to the bottom of the column and then both motors are stopped. The operator is now able to open the safety screen and remove the pallet. (i) With reference to Fig. 1(a) select and justify one specific metal from which the box section housing support could be constructed. [2] (ii) State four main properties which make PVC suitable for the window of the safety screen. [2] (iii) Using the answer booklet briefly compare two main but different performance specification points relating to the motor/gearbox A in comparison to motor/gearbox B. [4] (iv) Using annotated sketches briefly outline two methods that may be used to detect when the housing has reached the top and bottom position of the column. [4] A2V3S6 1629 2 [Turn over (v) On the pro forma provided (answer number 1(a)(v) or 1(b)(v)), use electronic and microelectronic circuit diagrams with annotation to produce a viable solution for each of the specified points stated below. (N.B. All brackets, housings, screws, nuts and bolts are not required) Design a circuit, which allows the operator to start motor/gearbox A only when the safety screen is positioned in front of the table and the housing is at the bottom of the column. [4] Motor/gearbox B is to be started 5 seconds after motor/gearbox A is started. Design a circuit to meet this requirement. [5] A2V3S6 1629 A microswitch is used to detect each revolution of the table. Design a circuit that will produce a single output pulse for each revolution of the table. Then design a system that uses this output pulse to count and display the number of turns of the table from the starting of motor/gearbox A until the film is cut. The maximum count is to be 99. [12] If the boxes are not stacked neatly it is possible that the stack could wobble during the wrapping process resulting in some of the boxes at the top of the stack becoming loose. Design a circuit which can detect this condition and initiate an alarm which will ring continuously until it is reset. [5] 3 [Turn over For candidates studying Pneumatic and Mechanical control systems answer part (b) using the pro forma (answer 1(b)(v)) and an answer booklet. (b) The insert Fig. 1(b) shows the latter stage of a prototype packaging line where a batch of crisp boxes, stacked on a pallet, are to be wrapped with cling film. After the pallet is set on the table by a forklift truck the operator takes the end of the cling film and then secures it to a crisp box before closing the safety screen. The wrapping sequence begins with motor/gearbox A rotating the table at a fixed speed and then motor/gearbox B slowly moving the housing up the column. On reaching the top of the column motor/gearbox B then slowly moves the housing down. When the housing is half way down the column an arm, containing a heated element, rotates through 60 degrees to cut the cling film, and then returns to its initial position. The sequence ends once the housing is returned to the bottom of the column and then both motors are stopped. The operator is now able to open the safety screen and remove the pallet. (i) With reference to Fig. 1(b) select and justify one specific metal from which the box section housing support could be constructed. [2] (ii) State four main properties which make PVC suitable for the window of the safety screen. [2] (iii) Using the answer booklet briefly compare two main but different performance specification points relating to the motor/gearbox A in comparison to motor/gearbox B. [4] (iv) Using annotated sketches briefly outline two methods that may be used to detect when the housing has reached the top and bottom position of the column. [4] A2V3S6 1629 4 [Turn over (v) On the pro forma provided (answer number 1(a)(v) or 1(b)(v)), use pneumatic and mechanical circuit diagrams with annotation to produce a viable solution for each of the specified points stated below. (N.B. All brackets, housings, screws, nuts and bolts are not required) Design a gearbox for motor A using the minimum number of gears and with only teeth between 20 and 100 that will enable the pallet to rotate once every 10 seconds from an input speed of 360 rpm. Then design a gearbox for motor B using the minimum number of gears with only teeth between 20 and 60 which will enable the cling film, measuring 250 mm in height, to move vertically to cover the boxes standing at 1.75 m, with minimum waste. The motor has an input speed of 360 rpm and the column has 4 teeth per 10 mm. (Show all calculations and state clearly the number of teeth for each of the gears on all shafts.) [12] 1629 Using an annotated sketch design a suitable housing and arrangement around shaft A which would prevent oil leakage from the gearbox. Name the parts used (see exploded view.) [5] A2V3S6 Using the output shaft of motor/gearbox B, design a suitable mechanism that will move the housing up and down the column (see exploded view). [4] Design a suitable mechanism attached to the column support that will rotate the arm containing the heated element through 60 degrees and return (see exploded view). [5] 5 [Turn over Section B Electronic and Microelectronic Control Systems Answer both questions in this section. 2 (a) Seven segment displays are available in two types, common anode and common cathode . Briefly explain: (i) the difference between these types of display; [2] (ii) the purpose of the seven resistors shown in Fig. 2. [2] S2 S1 Liquid Logic Circuit A B BCD to 7C segment D decoder S0 0V 0V Fig. 2 (b) An indication of the amount of liquid in a container, as shown in Fig. 2, is to be shown on a 7-segment display. The display shows 0 , 1 , 2 and 3 according to the following conditions: 0 when level is below S0, 1 when level is between S0 and S1, 2 when level is between S1 and S2 and 3 when level is above S2. Each sensor outputs logic 1 when it is in contact with the liquid. (i) Draw up a truth table relating the logic signals from the sensors and the outputs A and B from the Logic Circuit. [5] (ii) Deduce minimised logic expressions for A and B. [4] (c) When the liquid level is below sensor S0 it is proposed that the LED display should flash on/off to draw attention to this condition. Draw a block diagram to achieve this. A2V3S6 1629 [6] 6 [Turn over 3 (a) The thermistor is a device which can be used as a sensor in the measurement of temperature. State the principal physical property of the thermistor that is utilised in temperature measurement. [2] (b) (i) Briefly explain the purpose of connecting the thermistor (Rth) in series with resistor Rs as shown in Fig. 3. [1] 6V Rth o/p1 PIC o/p2 Rs V1 500 0V Fig. 3 (ii) The thermistor has the resistance values of 1000 at 10 C and 200 at 25 C. Calculate the corresponding values of voltage V1. (c) The circuit Fig. 3 is to be used to monitor and control the air temperature of a greenhouse. The voltage range of the analogue port of the PIC, is from 0 V to 6 V and the corresponding digital value ranges from 0 to 255. Find the digital values corresponding to 10 C and 25 C. [2] [4] (d) When the air temperature is above 25 C a ventilator is to be opened and when the air temperature is below 10 C an electric heater is to be turned ON. The ventilator is operated by a 24 V DC solenoid and the heater operates at 230 V mains. (i) Draw a suitable circuit which could be used to interface either the heater or the solenoid to an output port of the PIC. [6] (ii) Draw a flowchart of a subroutine that can be used to monitor and control the air temperature at 5 minute intervals, assuming that the heater is connected to o/p1 and the solenoid to o/p2. [4] A2V3S6 1629 7 [Turn over Section C Mechanical and Pneumatic Systems Answer both questions in this section. 4 (a) (i) Describe one main characteristic of a low viscosity oil. [1] (ii) State a suitable oil classification number for an application involving little pressure. [1] (b) Fig. 4(a) opposite shows a large rotating wheel being driven/turned by a small driving wheel. The small driving wheel is attached to a gear system as shown in Fig. 4(b) opposite. (i) Calculate the output torque on gear D if there is an input torque of 250 Nm on gear A. [3] (ii) The large rotating wheel and shaft which runs on plain bearings has a torque of 1.25 Nm. Calculate the work done against friction after 500 revolutions. [3] (iii) Gear A rotates at a speed of 240 rev/min with a torque of 250 Nm. Calculate the power supplied by the motor to gear A. [4] (c) Using an annotated sketch, name and draw in your answer booklet a clutch which could transmit motion from shaft X to shaft Y once shaft X reaches a speed of approximately 1500 rev/min. [4] (d) Using an annotated sketch, name and draw in your answer booklet a coupling which could link shaft Y to shaft Z, taking into account that shaft Z is likely to experience some axial movement from side to side. [3] A2V3S6 1629 8 [Turn over Large rotating wheel Gear system Small driving wheel Fig. 4(a) A 30 Teeth Motor C 30 Teeth B 120 Teeth D 120 Teeth Small driving wheel Shaft Z Axial movement Shaft X Shaft Y Fig. 4(b) A2V3S6 1629 9 [Turn over 5 Fig. 5 opposite shows part of an incomplete control system. (a) With reference to the diagram briefly state what is meant by the term positive feedback technique when applied to pneumatic systems. [1] (b) Briefly describe two main reasons why pneumatics may be preferred to hydraulics in control systems. [2] (c) The control system performs the following sequence after the START three port valve is activated: Cylinder A outstrokes. Cylinder B outstrokes. Cylinder A instrokes. Cylinder B instrokes. Cylinders C1 + C2 outstroke. Cylinders C1 + C2 instroke. (i) State the pneumatic sequence. [1] (ii) On the pro forma provided (answer number 5(c)(ii)), draw a suitable interlocking/ cascade sequential pneumatic circuit to achieve the desired sequence. [11] (d) Cylinder A has a stroke length of 100 mm and produces a force during the outstroke of 600 N. Assuming an efficiency of 95%, calculate the total work done on the outstroke. [4] A2V3S6 1629 10 [Turn over A2V3S6 1629 11 [Turn over 5 1 3 S TA R T 12 4 2 A 14 12 5 4 1 3 2 B Microswitch Fig. 5 14 12 4 5 1 3 2 C1 C2 14 S 9/05 1200 302507(101) [Turn over 1 15.9.05BP 3 12.12.05EA Safety screen 2 2.11.05EA A2V3S6 Fig. 1(a) Motor/gearbox B Housing Box section housing support Column 1629IN1 A2V31IN1 Direction of rotation Motor/ gearbox A Cling film for wrapping Table Part plan view of stack Heated element For candidates studying Electronic and Microelectronic control systems 4 23.1.06HF Pallet GCE Advanced Technology and Design Assessment Unit A2 3 Summer 2006 (for use with Question 1(a)) Do not write your answers on this insert [Turn over 1 15.9.05BP A2V3S6 1629IN1 Motor/ gearbox B moves up and down the column Column Fig. 1(b) Plan View pin 60 Angle which arm Box section column needs to move support Motor/gearbox B Housing Box section housing support Column Output shaft A Housing Motor/ gearbox A Cling film for wrapping Heated element For candidates studying Pneumatic and Mechanical control systems 4 23.1.06HF Output shaft 3 12.12.05EA Safety screen 2 2.11.05EA Table Pallet GCE Advanced Technology and Design Assessment Unit A2 3 Summer 2006 (for use with Question 1(b)) Do not write your answers on this insert [Turn ove[Turn over A2V3S6 1629 IN2 Question No. 1(a)(v) or 1(b)(v) A2V31IN2 Pro forma answer page (answer number 1(a)(v) or 1(b)(v)) ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 Summer 2006 Candidate Number 71 Centre Number A2V3S6 1629 IN3 Question No. 5(c)(ii) 5 1 2 3 START ST A R 12 14 4 A 14 12 12 4 1 3 1 14 2 A2V31IN3 Pro forma answer page (answer number 5(c)(ii)) 5 2 B Microswitch 14 12 ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 Summer 2006 4 5 1 3 2 C1 C C2 14 12 Candidate Number 71 Centre Number

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Additional Info : Gce Technology and Design May 2007 Assessment Unit A2 3, Unit 6: Systems and Control in Product Design
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