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  • Rotary to Reciprocation Motion

    Discussion in 'The main mechanical design forum' started by Samuelg, Jan 25, 2011.

    1. Samuelg

      Samuelg New Member

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      Had a little design problem crop up to convert rotary to reciprocating motion in that the unit must go sideways and return like a sawing motion. Used a pinion with teeth on top half and none on bottom engaging a rack on top and a rack below, both racks joined at ends. Pinion rotates teeth move the top rack, disengages and teeth then mate with lower rack sending it back.Any one else got any bright ideas or do I need to explain further. A drawing is worth a 1000 words.
      Regards
      Sam
       
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    3. AndrewNew

      AndrewNew Well-Known Member

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      Hi Sam,

      More common would be a crank-and-slider arrangement, I would think. With your design you are going to see pretty high inertial forces as the motion reverses (I think your reciprocating motion will be a "triangle" waveform) whereas with a crank and slider it is a sinusoid with nice smooth acceleration and decceleration of the load. I've a suspicion you might also get "crashes" if there is load on the racks during the "handover".

      Cheers

      Andrew
       
    4. dsgn2mfg

      dsgn2mfg Member

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      In the aluminum can making industry two linkages prevail for converting rotary to reciprocating motion, the Watts Linkage and the Diamond Linkage. The diamond linkage is far superior and can produce straight line motion within .005" in 8" of travel with no waste travel. The Watts link provides straight within .06"/8 but has a lot of waste travel to achieve this. I strongly suggest trying a diamond linkage connected to your crank or cam driven.
       
    5. Ivan_the_4th

      Ivan_the_4th New Member

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      Maybe a scotch yoke arrangement might suffice.
      You say that a picture is worth a 1000 words...Check out http://www.mechanisms101.com
      There is an animations menu on the home page that may provide you with the inspiration you need.

      Good hunting
       
    6. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      Have you considered a "scotch yoke" mechanism? This would provide a single axis (straight-line) reciprocation with minimum mechanical complexity.

      If your desired path requires a 2-axis motion, an orthogonal combination of scotch yokes may provide the desired motion.

      Describing your desired output path may clarify things. A 4-bar linkage may be needed if the path is complex.

      Source
       
    7. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      In the aluminum can making industry two linkages prevail for converting rotary to reciprocating motion, the Watts Linkage and the Diamond Linkage. The diamond linkage is far superior and can produce straight line motion within .005" in 8" of travel with no waste travel. The Watts link provides straight within .06"/8 but has a lot of waste travel to achieve this. I strongly suggest trying a diamond linkage connected to your crank or cam driven.

      Source
       
    8. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      Hi, Just saw this. It is difficult to make a judgement with so little info.
      What is the function of the linear motion.?
      Do you have to convert rotary to linear.?
      Can you use pneumatics.?
      Could you use a double acting rodless cylinder to give the linear movement.?

      Source
       
    9. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      This is a difficult one to envision without at least a sketch. However, my initial thought when converting rotation to reciprocation was to use a cam. Could this be a possible option?

      Source
       
    10. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      If you want to convert the rotational motion to translatory motion in the same plane then you go for Scotch yoke mechanism, otherwise if you want this thing in the perpendicular plane then you go for the rack mechanism that you yourself thought of (just see the racksteering mechanism, you would get lot of idea)

      Source
       
    11. pcdcox

      pcdcox Member

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      Hi Sam, I expected to get a reply from you by now.

      I have been thinking about your proposed method.
      i.e. A half pinion driving a top and bottom rack.
      If you want or have to do this I would add some sophistication into the design.
      I would use two(2) half pinions linked together and adjustable.
      One pinion would drive the lower rack and the other the upper rack.
      Each rack to be the same width as each pinion.
      The speed would be important. If it is sedate speed that would be advantageous.
      I would have adjustable shocks at each end of the stroke and I would also consider adjustable torsion springs on the pinions to absorbe the sudden reversal of direction.The torsion springs would help to absorbe shock and allow the first involute tooth to engage and the last tooth of the driver pinion to escape from engagement.

      You would obviously fit and adjust by hand until all interferance was eliminated.

      If you try this please let us know how it works out.
       

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