The offset slider crank mechanism also referred to as quick return mechanism has its application in shaper machines used in surfacing workpieces.
The advantages of this mechanism to a simple slider crank mechanism are that it allows for a slower forward stroke of the slider to and a faster return stroke.
With this idle time (the time when the machine is not performing cutting) is reduced. Let’s take a look at a simple demonstration of how this mechanism operates using a basic representation of crank, slider, fixed frame and coupler. Using a velocity plot, we will be able to see the variation of velocity throughout the cycle.
It is important to know that in this process the mechanism transforms rotary motion to linear motion.
We begin by creating the parts making the mechanism. We begin with the fixed frame. Below is the sketch of the part and the extruded model.
Extrude through 15mm.
For the crank, the sketch is as shown. Remember that the crank is the link in the mechanism that performs a full 360 degrees rotation of the fixed member.
The coupler geometry is quite similar to that of the crank with the difference being the lengths of the links. The sketch is as shown.
Lets create a simple block to represent the slider.
Once we have created the members we can go ahead to create the assembly and setup the appropriate constraints.
Remember that for the constraint between the slider and the frame we need to specify an offset distance of your choosing.
I went with 130mm offset distance for this particular demo.
Next, we need to setup the motion study. Under Motion, in the study define a rotary motion of 200rpm at the crank frame joint. Switch to Motion Analysis in order to start the study.
Next, specify that you want to analyze the motion of the slider then run the motion study.
Click on the results tab and select show Velocity Plot. Here we can see how the velocity changes with the stroke.
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