ME 358 Straight Line Mechanism Design

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ME 358Straight Line Mechanism Design Analysis

• TEAM SDSL
• Sudesh A. Woodiga
• Shahmi Ismail
• Deepak Ravindra
• Lau Kar Seng

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ABSTRACT

• The objective of this project was to design a
  crank mechanism which would translate a motor
  input into a straight line output.
• A grashof crank rocker was designed and mated
  with a modified Roberts straight line linkage to
  produce the desired output.
• Analysis was done at 5 different positions
  using working model and the analytical model
  learnt in class. The results obtained for each
  method have been tabulated separately.

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• INTRODUCTION

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INTRODUCTION

• After much research into the design of a
  mechanism for the given requirements, we decided
  that it would be best to go with a reference
  approximate straight line mechanism and the one
  selected was the Roberts straight line linkage.
• The only shortcomings of the selected mechanism
  was that it was a double rocker mechanism and
  that the output it produced was an approximate
  straight line.
• To feed the motor input we designed a four bar
  crank rocker mechanism which was mated to the
  Roberts mechanism. The crank portion would
  receive the motor input and the rocker mechanism
  would drive the double rocker Roberts mechanism.
  We also had to make sure that the point that
  moves along the output path does not exceed the
  specified velocity. The other problem was
  producing a straight output. After much thought
  and observation it was clear that the triangular
  link of the Roberts mechanism had to be
  lengthened in height to push the curvature in the
  path of travel of the vertex of the triangular
  link out and away from the 9 inch path. After
  much tweaking we managed to produce an almost
  perfect straight line in the 9 inch output path
  with a deviation of 0.01 inches in the x-axis
  path of travel, of which we think is adequate for
  this design.

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INTRODUCTION

• The next slide shows a CAD schematic of our
  mechanism with the positional as well as the
  packaging specifications being met.

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INTRODUCTION
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• ANALYSIS

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ANALYSIS

• In deciding the scope of the analysis, the
  group carried out an in depth discussion. It was
  decided that the point P on the linkage being the
  output path would be the focus of analysis
  because it was the focus of the design, being
  constrained by its required position and
  velocity.
• Two types of analyses will be presented, the
  first being the Working Model simulation analysis
  and the second being the analytical equations
  method learnt in class. The equations method
  will be used to cross check the results obtained
  from the simulation as well as enforce the
  validity of the equations method.

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ANALYSIS (SIMULATION)

• The model of the mechanism was created in
  working model and meter outputs were created
  while the simulation was running to monitor the
  output of the mechanism. The mechanism was
  designed and modeled as 2 four bar mechanisms to
  ease analysis. The output data was then copied
  to Excel and analyzed to be compared with the
  calculated values.

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ANALYSIS (EQUATIONS)
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ANALYSIS (EQUATIONS)
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ANALYSIS (EQUATIONS)
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ANALYSIS (EQUATIONS)
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• RESULTS

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RESULTS (SIMULATION)Point P
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RESULTS (SIMULATION)Four Bar 1
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RESULTS (SIMULATION)Four Bar 2
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RESULTS (EQUATIONS)
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RESULTS

• The next slide contains an animation of our
  mechanism with output meters for reference.

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RESULTS
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RESULTS (ANALYSIS)

• After examining the tables, the results
  obtained from the calculations turn out close to
  those obtained from the simulation.
• The results for the position, velocity and
  acceleration analysis for point P clearly show
  that it moves in a straight line with very slight
  and almost negligible deviation in the horizontal
  axis.
• This verifies the validity of our mechanism as
  well as the validity of the calculations method.
  This reinforces the confidence of the group on
  our approach to a mechanism related problem, from
  a design as well as analysis point of view.

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CONCLUSION RECOMMENDATIONS

• This project helped us apply the knowledge
  gained in class to a real world problem.
• The simulation method helped us form a visual
  concept of the mechanism as well as making it
  easier for us to see the effects of manipulating
  the geometry of the mechanism on its output.
• The analytical method assisted in verifying the
  results obtained from the simulation method. It
  also acts as a tool in which outputs can be
  calculated immediately with the change of
  geometry of the mechanism although its only
  weakness being a lack of visualization.
• The results we obtained from both methods came
  out close to each other with a slight difference
  due to round off errors.
• We as a group feel that we have received the
  optimum performance from this mechanism. We did
  however come across information in the text with
  regards to straight-line mechanisms. It was
  stated that for a perfectly straight output to a
  crank input the mechanism has to be at the very
  least a 6 bar 7 joint mechanism. This would lead
  to a complete redesign of our mechanism and would
  increase the complexity of the analysis
  performed.
• Overall we feel the project has been a success
  and we have applied the knowledge gained in class
  to produce a satisfying outcome to a real world
  problem.

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RESOURCES

• Design Of Machinery, Robert L. Norton, Third
  Edition, Mc-Graw Hill 2004
• http//www.brockeng.com/mechanism/