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

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ADVANCED General Certificate of Education 2007 Technology and Design assessing Unit 6 Systems and Control in Product Design A2V31 Assessment Unit A2 3 [A2V31] WEDNESDAY 30 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 Questions 4(b), 4(c), 5(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. A2V3S7 2726 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 parts (a)(i) to (iv) in the answer booklet and part (v) on the pro forma. 1 (a) Pick and Grab amusements, found in foyers of shopping and leisure centres, can challenge a person s dexterity. Insert Fig. 1(a) shows a prototype of such an amusement where the objective of the machine is the picking up of a toy by the Grab, controlled by the user, and then releasing it into a chute. The following sequence begins after a coin is inserted and the user presses the START button on the Control Panel: A pre-recorded music theme is played and small polystyrene balls are blown around the chamber for sound and visual effects. The user controls the X-axis and Y-axis motors to position the Grab plate approximately over the toy selected. When the LOWER button is pressed the Grab head is then slowly lowered; the user can position the Grab over the toy selected. When the GRAB button is pressed the toy is gripped and automatically raised towards the Grab plate. The user moves the Grab plate over the chute and on pressing the GRAB button again the toy is released. (i) Outline two main safety points which the manufacturer would need to consider regarding the working conditions for the XY control mechanism. [2] (ii) Give two main reasons why stainless steel would be used for the chute. [2] (iii) Briefly outline how the chute would be fabricated from a sheet of stainless steel material. [3] (iv) Using annotated sketches briefly outline two alternative methods that could be used to determine the limit of travel for the motors for the X- and Y-axis. [4] A2V3S7 2726 2 [Turn over (v) On the pro forma provided (answer number 1(a)(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) Design a circuit that will switch on the pre-recorded music and the blower for the polystyrene balls for a period of 1 minute 15 seconds after a coin has been detected and the START button pressed. Assume that both pieces of equipment operate at mains voltage. [5] Once the START button is pressed the amusement machine will run for a maximum time of 1 minute. Design a circuit to show the time in seconds that has elapsed after pressing the START button. Assume that pulses of 1-second repetition rate are available. At the 60th pulse the counter is to display 60 continuously. [5] The levers controlling the X-axis and the Y-axis motors each have three positions (1 2 3) as shown on the Control Panel of Fig. 1(a). The levers automatically return to position 2; when the lever is moved to position 1 the Grab plate moves away from the shown reference position and conversely for switch position 3. The Grab is lowered at a constant rate when the LOWER button is pushed. The Grab s position over the selected toy can be fine tuned by operation of the X-axis and the Y-axis motors. Design a circuit to control the X-axis and the Y-axis motors, taking into account the solution to Question 1(a)(iv). Your solution should include a means of preventing the X-axis and Y-axis motors operating at the same time. [12] The gripping action of the Grab is activated by a solenoid. When the GRAB button is pressed the solenoid is turned ON and remains ON until the GRAB button is pressed again to release the toy. Design a circuit that can provide a signal to control the action of the solenoid in response to the pressing of the GRAB button. [5] A2V3S7 2726 3 [Turn over For candidates studying Pneumatic and Mechanical control systems answer parts (b)(i) to (iv) in the answer booklet and part (v) on the pro forma. (b) Pick and Grab amusements, found in foyers of shopping and leisure centres, can challenge a person s dexterity. Insert Fig. 1(b) shows a prototype of such an amusement where the objective of the machine is the picking up of a toy by the Grab, controlled by the user, and then releasing it into the chute. The following sequence begins after a coin is inserted and the user presses the START button on the Control Panel: A pre-recorded music theme is played and small polystyrene balls are blown around the chamber for sound and visual effects. The user then selects from the control panel, one of four positions for the XY motors to move to. The Grab head is then lowered. The user can then decide if they want the table to make a small rotation. The Grab closes and the Grab head rises. The XY motors move the Grab head across to the release position, where the Grab opens and the toy drops into the chute for collection. (i) Outline two main safety points which the manufacturer would need to consider regarding the working conditions for the XY control mechanism. [2] (ii) Give two main reasons why stainless steel would be used for the chute. [2] (iii) Briefly outline how the chute would be fabricated from a sheet of stainless steel material. [3] (iv) Using annotated sketches briefly outline two alternative methods that could be used to determine the limit of travel for the motors for the X- and Y-axis. [4] A2V3S7 2726 4 [Turn over (v) On the pro forma provided (answer number 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) Design a pneumatic system that will detect the presence of the coin and begin the sequence when the START button is pressed. A time delay is created before lowering the Grab head slowly by 150 mm. Another time delay is created to allow the user to decide if they want the table to make a small rotation. Whatever the decision, the Grab closes slowly and then rises 150 mm. [12] 2726 Design a suitable Grab linkage that will attach to the plate and will be able to be opened and closed. [5] A2V3S7 Design a gearbox for motor X that will move the motor carriage 250 mm in 5 seconds, to the right given that the rack has 400 teeth per metre. The input speed from the motor is 2400 rpm and the output gear has 20 teeth. Use only gears with teeth between 20 and 100. [5] Design a suitable pneumatic system that will blow the polystyrene balls at low pressure around the chamber when the START button is pressed and finish when the Grab is directly above the chute. [5] 5 [Turn over Section B Electronic and Microelectronic Control Systems Answer both questions in this section. 2 (a) A symbol of an S-R latch is shown in Fig. 2(a). Briefly describe the operation of the latch with reference to the inputs S and R and outputs Q and Q. [4] S Q S-R Latch R Q Fig. 2(a) (b) The logic circuit shown in Fig. 2(b) detects the occurrence of pulses of short duration on the lines A, B and C. The output signals on o/p1, o/p2 and o/p3 are determined by the following conditions: A pulse on any input line outputs logic 1 on o/p . 1 Two coincident pulses on any one/single input line outputs logic 1 on o/p . 2 Three coincident pulses outputs logic 1 on o/p . 3 R A Latch B Latch C Latch o/p1 i/p1 R i/p2 i/p3 Logic Circuit o/p2 R o/p3 LEDs Reset o/p4 0V Fig. 2(b) (i) Briefly explain the purpose of the latches in this circuit. [2] (ii) Draw a truth table relating the inputs i/p1, i/p2 and i/p3, and outputs o/p1, o/p2 and o/p3. [3] (iii) Deduce logic expressions for outputs o/p1, o/p2 and o/p3. [3] (c) The logic circuit is to be replaced by a PIC. Write a programme which will read the inputs every second and determine which pulses have been received since last reading [7] and output appropriate signals on o/p1, o/p2 and o/p3. A2V3S7 2726 6 [Turn over 3 (a) (i) Phototransistors are devices used in electronic circuits for the detection of light. Briefly explain their mode of operation. [3] (ii) In Fig. 3(a) it is found that the current I is proportional to the intensity of light falling on the phototransistor Tr. Sketch how voltage Va varies with light intensity. [2] Vs Tr I Va Rs 0V Fig. 3(a) (b) A student investigating how light intensity from a light source varies with distance has set up the system shown in Fig. 3(b). The detector is the phototransistor shown in Fig. 3(a). It is found that when the bulb is closest to the detector the voltage Va is 100 mV. Enclosure Bulb Phototransistor D Stepper motor Track Fig. 3(b) (i) An analogue signal proportional to the intensity of light is required. Design an amplifier, based on an opamp, which can amplify the 100 mV to + 5 V. (Voltage gain Av is Rf/R for the inverting amplifier and 1 + Rf/R for the non-inverting amplifier; Rf is the feedback resistor). [4] (ii) The light source is moved by a stepper motor a distance of 20 cm in 1 minute and requires 100 pulses to move 1 cm. A 555 timer generates the pulses for the stepper motor. The pulse period T = 0.7C(R1 + 2R2). Find the resistor values when C = 1.0 F and R1 = R2. [5] (c) An analogue signal proportional to the distance D is required. The pulses from the 555 timer in conjunction with an 8-bit binary counter and a digital to analogue converter, DAC, are to be used. Suggest with the aid of a block diagram, a circuit to generate the required analogue signal. [5] A2V3S7 2726 7 [Turn over Section C Pneumatic and Mechanical Control Systems Answer both questions in this section. 4 Fig. 4(a) shows a cam and follower intended to form part of a display. The cam rotates in a clockwise rotation and the roller follower is offset to the right of the cam centre line by 10 mm. Cam Centre Line Roller follower Cam 10 mm Offset Fig. 4(a) (a) Name and sketch one other follower apart from a knife edge or roller which can be used with cams. [1] (b) On the pro forma provided (answer number 4(b)), construct a performance/displacement diagram which would accurately produce the following motion: A2V3S7 2726 0 120 rise 50 mm with uniform acceleration and retardation 120 180 rise 10 mm with uniform velocity 180 360 fall 60 mm with simple harmonic motion. Use a scale of 1 mm to 1 mm. 8 [6] [Turn over (c) On the pro forma provided (answer number 4(c)), using appropriate formal drawing techniques, construct a cam profile which would accurately follow the performance/ displacement diagram as shown in Fig. 4(b). The diameter of the roller follower is 10 mm and the minimum cam diameter is 40 mm. [6] Displacement 60 mm 0 mm 0 90 180 270 360 Angular Rotation/Degrees Fig. 4(b) (d) The cam rotates at 120 rev/min with a torque of 1.5 Nm. Calculate the power expended. [3] (e) A photographer wants to take pictures of the display and intends to mount a camera on a tripod which uses a ball and socket mechanism. Using an annotated sketch outline the main features of a typical ball and socket mechanism. [3] A2V3S7 2726 9 [Turn over 5 (a) Fig. 5(a) shows part of a mechanical system being modelled. (i) Briefly describe the term pitch point associated with gears. [1] (ii) Using an annotated sketch briefly outline how gear N could be connected to gear G enabling the direction of rotation of gear N to be changed quickly. [3] (iii) Calculate the velocity ratio between gear A to gear M. A2V3S7 2726 10 [4] [Turn over A2V3S7 2726 11 [Turn over L Diameter 90 mm M 70 Teeth G 60 Teeth H 25 Teeth K Diameter 45 mm Fig. 5(a) Gear N F Diameter 100 mm E Diameter 50 mm C 80 Teeth J 60 Teeth D Wormwheel 60 Teeth B 80 Teeth A 160 Teeth Motor (b) Fig. 5(b) shows part of the pneumatic circuit being modelled. It is intended to perform the following sequence once the Start valve is switched: Cylinder A outstrokes. Cylinder B outstrokes. Cylinder A instrokes. Cylinder B instrokes. On the pro forma provided (answer number 5(b)) complete the desired sequence using the components provided. [5] (c) Pneumatic circuits can incorporate 4 group interlocking changeover systems. (i) Briefly explain one advantage and one disadvantage associated with the use of interlocking in sequential circuits. [2] (ii) On the pro forma provided (answer number 5(c)(ii)) draw a four group interlocking changeover control system which could be used in an appropriate circuit. [4] A2V3S7 2726 12 [Turn over 2 1 Fig. 5(b) 1 2 2 12 12 4 4 5 5 1 1 3 3 2 2 14 14 B 1 2 1 Start A THIS IS THE END OF THE QUESTION PAPER A2V3S7 2726 13 [Turn over A2V3S7 A2V3S7 2726 14 [Turn over A2V3S7 A2V3S7 2726 15 [Turn over S 2V3S7 2726 A 4/06 7-075-1 16 [Turn over A2V3S7 2726.02 INS1 Grab plate Control panel Table Do not write your answers on this insert Chute Polystyrene balls Stainless steel chute Enlargement 1 Grab Grab head Motor controlling X-axis Motor controlling Y-axis Start button START 1 X 3 2 3 X lever 2 1 Y Y Lever GRAB LOWER Lower button Grab button Coin slot 1. 2. 3. 4. 5. Enlargement 3 Control Panel Motor to control movement along the X-axis Grab plate reference position Motor to control movement along the Y-axis Enlargement 2 Instructions Insert coin and press START button Use X and Y levers to move Grab over toy you choose Press LOWER button to start lowering the Grab Press GRAB button to pick up toy Move Grab over the Chute and press GRAB button to release toy Table For candidates studying Electronic and Microelectronic control systems Fig. 1(a) GCE Advanced Technology and Design Assessment Unit A2 3 Summer 2007 (for use with Question 1(a)) A2V31IN1 [Turn ove[Turn over A2V3S7 BM1F1 2726.02 INS1 Grab plate Control panel Do not write your answers on this insert 2 Chute Polystyrene balls Stainless steel chute Enlargement 1 Table Grab Grab head Motor controlling X-axis Motor controlling Y-axis B A C Grab plate reference position Motor to control movement along the Y-axis 250 Toy A Toy B Enlargement 2 D Start button START Toy D rotation of table Coin slot 3. 1. 2. Control Panel Enlargement 3 Toy C Press to activate rotation of table TABLE All dimensions in mm Motor to control movement along the X-axis 200 Pneumatics needed to move Grab arm Grab needed to open and close Enlargement 4 Instructions Insert coin and press START button Press either button A, B, C or D to move the arm and Grab directly above the toy you would prefer Wait until the Grab arm lowers then decide if you want to rotate the table slightly by pressing the table button. Grab head Grab plate For candidates studying Pneumatic and Mechanical control systems Fig. 1(b) GCE Advanced Technology and Design Assessment Unit A2 3 Summer 2007 (for use with Question 1(b)) [Turn over [Turn over

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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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