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GCE JAN 2007 : (A2 3) Systems and Control in Product Design

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ADVANCED General Certificate of Education January 2007 Technology and Design assessing Unit 6 Systems and Control in Product Design A2V31 Assessment Unit A2 3 [A2V31] MONDAY 8 JANUARY 2007, AFTERNOON 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 Questions 5(a)(ii), (b) 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. A2V3W7 2259 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 a prototype digger ride that could be used to entertain small children in a foyer of a shopping centre. Children are helped into the digger, the seat belt is fastened and the door is closed. The following sequence begins after coins are inserted at the control panel: As the coins pass through the slot they are detected. The bulb in the illuminated START switch is turned on. When the illuminated START switch is pressed the bulb in the switch is turned off and the ride motor will run. At the same time a light on the roof of the cab flashes on and off with a frequency of 2 Hertz. After a period of two minutes the sequence stops. (i) Determine if the sequence described above is that of an open-loop or closed-loop system. Using the answer booklet give one main reason in support of your answer. [2] (ii) Give two main reasons why each of the following materials is used. Box section mild steel for the frame Glass reinforced plastic for the shell of the digger. [4] (iii) Using annotated sketches briefly outline two alternative methods that may be used to detect that the seat belt has been fastened. [4] (iv) Outline two main safety points that the manufacturer would need to consider regarding the control circuitry. A2V3W7 2259 2 [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 that will fulfil each of the specified points stated below. (N.B. All brackets, housings, screws, nuts and bolts are not required) A2V3W7 2259 The voltage on a control line is +5 V. Design a circuit that will make the voltage drop for one second to 0 V (creating a negative pulse) when a coin is inserted at the control panel. [4] Design a circuit to switch on the bulb in the illuminated START switch when a coin is detected. The bulb should remain on until the START switch is pressed. [5] Design a circuit that will control the ride motor and the flashing light when the START button is pressed. The motor must run for a period of 2 minutes during which the flashing light operates at a frequency of 2 Hz. (The ride motor draws a current of 10 A when running and the flashing light operates from a 12 V supply). [12] The digger arm, shown in Fig. 1(a)(i), is raised or lowered at variable speed by movement of the lever as shown in Fig. 1(a)(ii). The movement of the lever is limited to that shown on the drawing where the speed of movement is determined by the position of the lever. Maximum speed is produced by maximum movement of the lever. Limit switches control the extent of up and down movement. Design a system to control the motor in this way. [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 a prototype digger ride that could be used to entertain small children in a foyer of a shopping centre. Children are helped into the digger, the seat belt is fastened and the door is closed. The following movement begins after money is inserted: The table supporting the digger moves to provide a reciprocating motion. Each corner of the table rises and falls in a sequence to provide a rocking motion. The exhaust lifts up and down. The digger arm produces an oscillating movement. (i) Determine if the sequence described above is that of an open-loop or closed-loop system. Using the answer booklet give one main reason in support of your answer. [2] (ii) Give two main reasons why each of the following materials is used. Box section mild steel for the frame Glass reinforced plastic for the shell of the digger. [4] (iii) Using annotated sketches briefly outline two alternative methods that may be used to detect that the seat belt has been fastened. [4] (iv) Outline two main safety points that the manufacturer would need to consider regarding the control mechanism. [2] (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 that will fulfil each of the specified points stated below. (N.B. All brackets, housings, screws, nuts and bolts are not required) A2V3W7 2259 Design a pneumatic system that will slowly lift and lower the exhaust pipe 100 mm continuously for the duration of the ride. [4] Using the output shaft of gearbox A, design a suitable mechanism that will reciprocate the table 50 mm to the left and right. Show how you would connect your design to both the shaft and the table. [5] By connecting the output shaft of gearbox A to shafts B and C, design a mechanism that ensures that each corner of the table will be lifted and lowered by 50 mm twice a minute in the following sequence: bottom right, top left, bottom left and top right. [12] Design a suitable mechanism driven from shaft D that will oscillate the digger arm through 45 degrees at half the speed of the rotation of shaft D. (20 rpm.) [5] 4 [Turn over Section B Electronic and Microelectronic Control Systems Answer both questions in this section. 2 (a) Five LEDs, a, b, c, d and e, are arranged in a column as shown in Fig. 2. The LEDs are controlled by the outputs of the logic circuit. As the output of the counter is incremented from 000 the LEDs are to be switched ON in the following manner, a, ab, abc, bcd, cde, de, e and all LEDs OFF. (i) Draw up a truth table for the counter outputs Qa, Qb and Qc as the counter is incremented from 000 to 111; Qa is the LSB. [2] (ii) Extend the truth table to include columns for A, B, C, D and E showing when the LEDs are ON; assume a 1 corresponds to an LED being lit. [4] (iii) Deduce minimised logic expressions for the outputs A, B and C. [6] (iv) Draw logic circuits for the minimised logic expressions. [3] (b) (i) Draw the waveforms of the outputs A, B and C of the logic circuit in Fig. 2 over a period of eight input pulses. [2] 1 (ii) A circuit generating continuous pulses with a frequency f = , drives the 2.1 (CR) counter in Fig. 2. Determine suitable values of C and R so that the switching sequence of the LEDs is repeated every second. [2] a Qa Clk 3 bit binary counter Logic Circuit Qb Qc A B C D E b c d e Fig. 2 A2V3W7 2259 5 [Turn over 3 (a) (i) Sketch the structure of a strain gauge and indicate the active axis . [1] (ii) State the principal property, which makes this device a suitable sensor for the measurement of strain. [1] (iii) Briefly state how the resistance of a strain gauge varies with temperature. [1] (b) The structure shown Fig. 3(a) is used to measure the vertical load W. Two strain gauges, Sg1 and Sg2, are attached to the topside and the underside of the cantilever arm as shown. The gauges are connected as part of a Wheatstone bridge as shown Fig. 3(b), where Rg1 and Rg2 represent the resistances of gauges Sg1 and Sg2 respectively. The values of Rg1 and Rg2 are each 120.0 when the sensors are unstrained. It is found by experiment that the resistance values of Rg1 and Rg2 are 120.4 and 119.6 respectively when the vertical load W is nominally 10 kg. Vertical load W Sensor Sg1 Sensor Sg2 Cantilever arm Fig. 3(a) Fig.3(b) 5V Rb R22 R Rg2 2 Rg Vref +VS R11 R o/p1 1 ADC V11 V R11 R Rb Rg1 Rg1 VS V22 V VO PIC o/p2 o/p 2 o/p3 o/p 3 R22 R 0V Fig. 3(b) Fig. 3(b) A2V3W7 2259 6 [Turn over (i) Briefly explain how this arrangement of gauges compensates for errors due to temperature change. Assume both strain gauges are subject to identical changes in temperature. [2] (ii) Calculate the voltages V1 and V2 when the gauges are strained. [2] (iii) Calculate the output voltage Vo of the amplifier when the gauges are strained. Output voltage Vo = R2/R1(V2 V1), R1 = 10 k , R2 = 500 k and Rb is 470 . [2] (c) The analogue to digital converter (ADC) in Fig. 3(b) has an 8-bit output and a reference voltage Vref of 1.25 V. (i) Briefly explain the meaning of the term 8-bit . [2] (ii) The decimal equivalent D of the ADC output is given by D = Vo(255)/Vref. Determine the value of D when the 10 kg load is present. [2] (d) The load W can vary and three separate output signals o/p1, o/p2 and o/p3 are required to indicate the following conditions: W < 9 kg, 9 kg W 11 kg and W > 11 kg. The PIC shown in Fig. 3(b) is programmed to determine these conditions. Draw a flow chart for the conditions stated above. A2V3W7 2259 7 [6] [Turn over Section C Pneumatic and Mechanical Systems Answer both questions in this section. 4 Fig. 4(a) shows part of a prototype lifting vehicle. The lifting arm is attached to a winch which raises and lowers the load using a cable. Cable Lifting arm Load Handle Winch Fig. 4(a) (a) (i) State one advantage and one disadvantage associated with using disc brakes in comparison to using a drum braking system in vehicles. [2] (ii) Using an annotated sketch outline the main features of a typical cantilever braking system. [3] (iii) During operation the handle on the winch shown in Fig. 4(a) had to be held securely or the cable could unwind backwards. Using an annotated sketch, briefly name and outline a possible method which could be used to prevent this unwanted backward movement yet allow unwinding when required. [3] (iv) The winch lifts a load with a mass of 50 kg up a vertical height and gains 1471.5 kJ in potential energy before coming to rest. Calculate the vertical height the load is lifted. Assume g = 9.81 m/s2 [3] (b) Fig. 4(b) opposite shows a linkage system. (i) State how the mechanical advantage of the linkage system could be reduced. [1] (ii) Calculate the moments produced by the springs about the pivot and deduce their overall effect on the linkage system. [3] (iii) The resistance to movement at R is 150 N. Calculate the size of the force F required to overcome the resistance. [4] A2V3W7 2259 8 [Turn over A2V3W7 2259 9 [Turn over 40 N F Spring 200 Spring 60 N Pivot Fig. 4(b) Pivot 150 150 N All dimensions are in mm R 200 100 200 300 5 Fig. 5 opposite shows part of a printing station used by manufacturers of wax polishing blocks. The heating element linked to cylinder D creates a design on the wax block when it is pressed onto it. Completed wax blocks are then released through the trap door and move onto the conveyor via the chute. (a) The conveyor uses a rolling element bearing and experiences radial and axial movement from both directions. (i) Briefly describe one advantage and one disadvantage associated with using a rolling element bearing in comparison to a plain bearing. [2] (ii) On the pro forma provided (answer number 5(a)(ii)) draw a suitable rolling element bearing arrangement for the conveyor shaft. Please note that significant axial forces are present in both directions. [3] (b) Once the block reaches the end of the conveyor it presses a switch S and activates cylinder P which pushes the block to another area. On the pro forma provided (answer number 5(b)) complete the electro-pneumatic circuit to achieve the desired function. [3] (c) The printing station performs the following sequence once the Start three port valve is activated: Cylinder A outstrokes to close the trap door. Cylinder B outstrokes to secure block 2 housed in the hopper. Cylinder C outstrokes slowly to push block 1 onto the trap door. Cylinder C instrokes. Cylinder D outstrokes to press the design onto the block. Cylinder D instrokes. Cylinder A instrokes slowly to open the trap door. Cylinder B instrokes. (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. [10] A2V3W7 2259 10 [Turn over A2V3W7 2259 11 [Turn over Cylinder A Trap Door Heating Element Cylinder D Hopper 1 2 Chute Fig. 5 Wax Block Cylinder B Conveyor Cylinder C S 12/05 800 9-009-1 [Turn over A2V3W7 Box section mild steel frame Digger arm Fig. 1(a)(i) Flashing light Glass reinforced plastic shell Coin slot Lever Insert Coins START 2259.02 A2V31IN1 Fig. 1(a)(ii) Control Panel Illuminated START switch For candidates studying Electronic and Microelectronic control systems Fig. 1(a) GCE Advanced Technology and Design Assessment Unit A2 3 January 2007 (for use with Question 1(a)) [Turn over A2V3W7 2259.02 Box section mild steel frame Glass reinforced plastic shell Table A Shaft C Shaft B Pivot point Partial Plan View On A A Bottom left Top left Digger arm Bottom right Top right Shaft D (20 rpm) Exhaust pipe Output shaft A 30 rpm Motorised gearbox A Front View For candidates studying Pneumatic and Mechanical control systems Fig. 1(b) A GCE Advanced Technology and Design Assessment Unit A2 3 January 2007 (for use with Question 1(b)) [Turn ove[Turn over Question No. 1(a)(v) or 1(b)(v) ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 January 2007 Centre Number 71 Candidate Number Pro forma answer page (answer number 1(a)(v) or 1(b)(v)) A2V3W7 2259.03 A2V31IN2 A2V31IN3 Question No. 5(a)(ii) ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 January 2007 Centre Number 71 Candidate Number Conveyor Shaft Conveyor Shaft Axial Movement Conveyor Pro forma answer page (answer number 5(a)(ii)) A2V3W7 2259.03 A2V31IN3 A2V31IN3 Question No. 5(b) Centre Number Centre Number ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 January 2007 71 71 Candidate Number Candidate Number P S 12 V 0V Pro forma answer page (answer number 5(b)) A2V3W7 2259.03 A2V31IN4 Question No. 5(c)(ii) Centre Number ADVANCED LEVEL TECHNOLOGY AND DESIGN Assessment Unit A2 3 Unit 6 January 2007 71 Candidate Number A 12 14 5 1 3 C B 14 12 5 1 12 14 5 3 3 1 D 12 14 START 5 1 Pro forma answer page (answer number 5(c)(ii)) A2V3W7 2259.03 A2V31IN5 3

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