Copyright © Loughborough University. All rights reserved. 1 MANUFACTURING AUTOMATION AND CONTROL 20WSC108 January 2021 (1b) Exam paper This is a (1b) online examination, meaning you have a total of 2 hours plus an additional 30 minutes to complete and submit this paper. The additional 30 minutes are for downloading the paper and uploading your answers when you have finished. If you have extra time or rest breaks as part of a Reasonable Adjustment, you will have further additional time as indicated on your exam timetable. You may handwrite and/or word process your answers, as you see fit. You may use any calculator (not just those on the University’s approved list). Page 1 of 6 /continued MANUFACTURING AUTOMATION AND CONTROL (20WSC108) January 2020 2 Hours Answer ALL THREE questions. Questions carry the marks shown. 1. a) A company is looking to automate the packaging process at the end of one of their production lines. Components are arriving on a conveyor and reach an end stop. A simple pneumatic actuator has been designed to push them into a crate for further transport. Each crate holds five components. A proximity sensor detects when a new component has arrived at the end stop (X3) and another sensor (X4) detect that a crate is in position. The crates are removed by an automated guided vehicle (AGV) when full. The interlock with the AGV system sends out a call (Y4) when the crate is full. The AGV confirms with X5 that the crate has been picked up. New empty crates are added manually. A light needs to be switched on to notify an operator that a new crate is needed. The process starts with through pushbutton activation (X1) and stops after completing filling the current crate when another button is turned off (X2). If no crates are available, the conveyor should be stopped and restart when a new crate is present. Table Q1a.1: List of inputs and output channels Inputs Description Outputs Description X1 X2 X3 X4 X5 Start pushbutton Off button Component at end stop Crate in position Crate picked up interlock from AGV Y1 Y2 Y3 Y4 Y5 Conveyor power (on/off) Extend pneumatic cylinder Contract pneumatic cylinder Crate is full interlock to AGV Crate empty light Develop the control logic for the crate filling system described above using sequential function chart notations based on IEC61131. Use the input and output symbols provided in Table Q1a.1. State any assumptions you are making. [10 marks] Page 2 of 6 /continued b) In a food processing plant, several similar items arrived individually packaged on a conveyor belt at a high rate in random locations. They need to be put into different boxed depending on their packaging. i. Recommend what kind of robotic system would be suitable for this kind of task and justify why using its key behaviour characteristics. [3 marks] ii. Suggest a suitable sensor system for this task and explain what information will be passed to the robot. [2 marks] c) Explain how a binary proximity sensor could be used to determine the correct size of an object e.g. the width of a box. Provide diagrams to illustrate the approach. Discuss potential limitations of this approach. [5 marks] 2. a) A newly developed control logic for a pneumatic pick and place machine is not working as expected. It has been designed using Ladder Logic for pick and place device consisting of two pneumatic cylinders and a pneumatic gripper (see Figure Q2a.1). The device was expected to pick up a component from location A and move it to location B by moving down to pick up the part, closing the gripper, going back up again, moving across, moving down, releasing the part, moving back up and finally moving back across. The trigger is the arrival of a new workpiece carrier on a conveyor (X1). The device needs to confirm to the conveyor that the operation is completed. All three pneumatic actuators are controlled through valves as shown in Figure Q2a.2. The list of sensor inputs and actuator outputs is given in Table Q2a.1. i. Use the Ladder Logic diagram provided (Figure Q2a.3 in the Appendix) to highlight errors in the logic and explain what the error is. [6 marks] ii. Provide solutions how to correct the errors in the programme. [6 marks] Page 3 of 6 /continued Figure Q2a.1: Schematic of pneumatic pick and place device Figure Q2a.2: Pneumatic diagram for pick and place device Table Q2a.1: List of input and output channels for pick and place device Inputs Description Outputs Description X1 X2 X3 X4 X5 Proximity sensor on conveyor Horizontal cylinder contracted Horizontal cylinder extended Vertical cylinder contracted Vertical cylinder extended Y1 Y2 Y3 Y4 Y5 Y6 Y7 Contract horizontal cylinder Extend horizontal cylinder Contract vertical cylinder Extend vertical cylinder Open gripper Close gripper Pick and place completed interlock b) An automotive company is considering whether to change their current hydraulic actuated resistance spot welding guns (tools) to full electric actuation. The guns are mounted at the end of large articulated arm robot with long arms to weld together the different panels of a car body. The gun needs to press together the two or Page 4 of 6 /continued three sheets of metal before a high current can be applied to weld them together in a spot. Make a recommendation based the respective advantages and disadvantages of hydraulic and electric actuation for this application. Explain your decision. [4 marks] c) A company is considering introducing a new automated production cell for one of their long-established products. The product is expected to have a daily demand of 10,000 units and run for at least another 5 years. The cell will need to automate several assembly steps to make the product. Recommend whether fixed, programmable, and flexible automation would be most appropriate approach for the above production cell. Justify your answer. [4 marks] 3. XPTO Technologies Ltd provides consultancy services for manufacturing processes. The company was approach by a client interested in exploring Petri Nets to model their processes. The client has created a Petri Net for one of their processes seen in Figure Q3a.1. Figure Q3a.1: Petri Net. a) Using the states (A,B,C,D,E,F,G,H), establish the Reachability graph for the Petri Net in Figure Q3a.1, and discuss its liveness. [7 marks] b) The client provides the sketch of a system in Figure Q3b.1. The system comprises of two robots, two part feeders, two machine Page 5 of 6 /continued centres, and a central conveyor. The feeders are expected to always have new parts ready as soon as the previous part has been picked up. Machine A and Machine B should only be reserved when in use. Each robot is designed to pick a part from a feeder and then place it in the machine. Once the machine is finished, the robot picks the part up again and when both robots are ready, they join the two parts together and place the finished product on the conveyor. Assume that the conveyor has a limited capacity of 3 and the robots should stop the creation of new products when the conveyor is full. Model a Petri Net of this system that results in this behaviour. [8 marks] Figure Q3b.1: Sketch of system layout. c) The client is requesting the design of an agent system for the scenario described in question 3b). Consider each separate machine (robots, feeders, machine centres and conveyor) as an agent. Assume that the Conveyor agent will be responsible for the coordination between the two robots. For this agent system, define the sequence diagram for the manufacture and assembly of one full product. [5 marks] N Lohse P Ferreira Robot X Feeder Part A Feeder Part B Machine Part A Machine Part B Conveyor Robot Y Page 6 of 6 Appendix Figure Q2a.3: Incorrect ladder logic diagram to mark errors X1 X2 X4 X5 S Y4 S Y6T1 1 sec. T1 S X4 X4 S Y2 X3 S Y4 T2 S Y3 X5 S Y6T2 1 sec. X4 S Y1
欢迎咨询51作业君