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Virtual Laboratory Kinematic Analysis and
Animation of a Cupboard Hinge

• Jacek Uziak - University of Botswana, Botswana
• John D.G. Foster - Carlisle College, U.K

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• Mechanical systems used in production processes
  may be divided into two separate groups.
• The first group comprises mechanical systems in
  which all elements are fixed (e.g. frames).
• The second group comprises systems in which the
  elements are connected movably mechanisms.
• The purpose of a mechanism is therefore to
  transmit motion and/or force from a source to an
  output element.

A linkage consists of links (or bars, or
elements), generally considered rigid, which are
connected by joints to form open or closed chains
/or loops). Such kinematic chains, with at
lease one link fixed, become mechanisms if at
least two other links retain mobility, or
structure if no mobility remains.
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• The techniques for finding the displacement
  velocities and accelerations fall into three
  broad groups
• graphical, analytical and numerical.
• (combinations of the above techniques also used)
  
• The graphical methods - very time consuming,
  analysis valid for a particular position of the
  mechanism.
• The same disadvantage applies for the velocity
  and acceleration diagrams - the semi-graphical
  methods
• The analytical technique - great advantage of
  giving a general solution, sometimes the amount
  of analysis and differentiation needed for simple
  mechanisms excessive
• The choice depends very much on the nature of
  the mechanism and the tools available, and is
  largely a matter or experience.

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• The analysis of planar linkages, studied in a
  Mechanics of Machines course, has always been
  quite a challenge for students.
• A semi-analytical approach (velocity and
  acceleration diagrams) is normally the major part
  of the syllabus in this subject.
• It is very time consuming
• Results are not easy to visualize
• It is usually difficult for the students to
  imagine the whole and complete solution and to
  draw conclusions for a particular mechanism.

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BEng Programmes at the University of Botswana

• University of Botswana operates on a typical
  credit system
• B.Eng. programmes (Mechanical, Electrical and
  Civil) extend over ten semesters after entry at
  the GCSE level, or eight semesters for those with
  A-level or Ordinary Diploma qualifications.
• Course credits over ten semesters are required to
  total 150, approximately 15 per semester.
• There are General Education Courses which take
  not more than 20 of total credits
• Choices within the home faculty courses permit
  students to select options for approximately 25
  of the 122 credits allocated to these courses.

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Mechanics of Machines in BEng (Mech)

• The Mechanics of Machines course is a core course
  in Year 3 of BEng programme in Mechanical
  Engineering.
• It follows a general Dynamics course in Year 2
  which is being taken by all engineering students
  (civil, electrical and mechanical - Year 2 is a
  common year for all engineering students).
• Course has a value of 3 credits and is covered in
  one 15-week semester in 2.5 hours of lecture, 1
  hour of tutorial and 1 hour of lab.
• Laboratory part of the course is done in groups
  of maximum 3 students. The labs are done on
  rotational basis which accommodates small groups
  but it also means that students have to do labs
  on topics which are yet not covered during
  lectures.

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Analysis of Planar Linkages

• Kinematic analysis of planar linkages forms just
  a part of the syllabus for Mechanics of Machines
  course.
• The method which is being used is the velocity
  and acceleration diagrams (with some elements of
  analytical method for simple mechanisms).
• The particular problem for the students is the
  difficulty in visualizing the motion of
  mechanisms.
• Lab part of the course is designed to complement
  the lecture part with particular emphasis on
  understanding of the subject matter.
• Kinematic analysis is one other topics which
  include balancing of rotating and reciprocating
  masses, gyroscopic action, gears and epicyclic
  gears, flywheel, vibrations, etc.

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Lab Exercise on Kinematic Analysis

• The particular objectives of the exercise on
  kinematic analysis are
• to help students to visualize the motion of
  different mechanisms,
• to make them aware of structures of different
  mechanisms,
• to make them aware of the advantages of using
  computer software for the analysis,
• to show to them that normally the use of the
  software is easy and that they should not be
  afraid of such tools,
• to familiarize them with a specific software.

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• Example
• Practical
• Preferably from every day use so the students of
  all background would have a feeling about it.
• With obvious and simple practical task
• Appropriate level of difficulty
• Relatively easy in terms of structure but with
  more than 4 links.
• Small
• Small in size so it can be taken to hand and
  manipulated with.
• Small and accessible so the dimensions can be
  easily measured.

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• Software
• Easy to use
• No advanced computer background required
• Easy to create models from basic components
• Ability to animate
• Animate the motion (continuous update on paths)
• Animate other selected parameters (continuous
  update on some vectors and graphs)
• Locate the instantaneous centres of rotation and
  watch them move through all their positions
  during animation
• Flexible
• Links with pivots or sliders
• Create a Report with possibility to export data
  to a spreadsheet (including all graphs) and to
  produce video file

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ROBERTS ANIMATOR 1.0
CUPBOARD HINGE
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• The objective of the lab is to identify the
  mechanism and to perform its kinematic analysis
  and animation.

• The mechanism is a popular cupboard hinge used
  especially in kitchen cupboards.

• Use the Robertson Animator to perform its
  kinematic analysis and animation.

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Lab Procedures

• The students are to carry out the following
  tasks.
• Identify the type of the mechanism count the
  number of links and joints.
• Measure the dimensions.
• Create the model of the mechanism using the
  software.
• Animate the mechanism and perform kinematic
  analysis assuming that crank rotates with a
  constant angular velocity.
• Produce a report with proper headings.
• Export results to Excel and save it.

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Model produced using the Roberts animator
Hinge

• Although it looks harmless it usually takes a
  lot of effort for students to
• identify properly this 6-link mechanism,
• to measure the necessary dimensions and
• to make the model using the software.
• The identification of the mechanism should be
  considered as important element of the whole
  exercise, also the identification of the input
  and output link, and the frame.

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General Screen for Analysis

• The properties of links and joints clearly
  specified in table
• The model drawn in the main area and the selected
  graph presented in the bottom area.
• By using the function buttons, it is possible to
  perform all possible features of the software

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Animation
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• Output to a Typical Spreadsheet (Excel)

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Conclusions

• The exercise has been successfully introduced in
  Mechanics of Machines course at the University of
  Botswana.
• It teaches students the basics of kinematic
  analysis of planar linkages.
• It applies the theoretical knowledge gained in
  classrooms to some practical applications in
  performing the kinematic analysis of an element
  known very well from every day life.
• The students are using existing commercial
  software to undertake the analysis and to produce
  the results together with conclusions and
  recommendations.
• The software allows them to visualize the motion
  of the mechanism (by animation), to analyze the
  kinematic properties of joints and links
  (positions, paths, velocities, accelerations) and
  to produce professional report.