Virtual Laboratory – Kinematic Analysis and Animation of a Cupboard Hinge

1. Virtual Laboratory – Kinematic Analysis and Animation of a Cupboard Hinge Jacek Uziak - University of Botswana, Botswana John D.G. Foster - Carlisle College, U.K

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. CHALLENGES SOFTWARE EXAMPLE

10. 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.

11. 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

12. CHALLENGES SOFTWARE EXAMPLE ROBERTS ANIMATOR 1.0 CUPBOARD HINGE

13. 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.

14. 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.

15. 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. Model produced using the Roberts animator Hinge

16. 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

17. Animation

18. Output to a Typical Spreadsheet (Excel)

19. 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.