程序代写案例-20WSC108

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

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