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The graphic on the right shows an enlarged view of a cam mechanism from the engine of a strimmer - Leaving Cert DCG - Question C-4 - 2017
Question C-4
The graphic on the right shows an enlarged view of a cam mechanism from the engine of a strimmer. A cam, similar to the one shown, imparts the following motion to a... show full transcript
Worked Solution & Example Answer:The graphic on the right shows an enlarged view of a cam mechanism from the engine of a strimmer - Leaving Cert DCG - Question C-4 - 2017
Step 1
Draw the displacement diagram for the cam.
Answer
To create the displacement diagram for the cam, follow these steps:
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Divide the diagram into 360°: Create divisions of 30° each to represent a total of 12 segments across the horizontal axis. Mark these divisions clearly on the x-axis of your diagram.
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Establish follower position (0°, 90°, 180°, 360°):
- 0° to 90°: Draw a straight line from 0° to 90° to represent the rise of 60mm. This corresponds to a vertical distance of 4 units on the diagram since each 30° represents 15mm.
- 90° to 180°: Draw a horizontal line from 90° to 180°. This represents the dwell period (no movement of the follower).
- 180° to 360°: For the fall of 60mm back to the starting position, draw a downward line from 180° to 360°, mirroring the rise, resulting in another straight line that descends to the 0mm mark.
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Uniform velocity: Ensure that the length of the rise matches the downward fall to maintain uniform velocity throughout the motion.
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Complete the diagram: Connect the points across the graph correctly to finalize the displacement diagram, ensuring clarity and accuracy.
Step 2
Draw the cam profile.
Answer
The steps to draw the cam profile are as follows:
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Identify the cam center and nearest approach: Mark the center of the cam, which is the point from which the cam rotates. The nearest point of the follower to the cam center is 35mm.
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Draw the camshaft: Specify the diameter of the camshaft as 16mm. This indicates the radius of the cam profile will be 8mm from the center.
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Account for rotation direction: Since the cam rotates in an anti-clockwise direction, represent the profile accordingly, adjusting the positions of points in the correct quadrants.
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Mark the angles corresponding to the displacement diagram: For each segment of the displacement diagram, plot the points at the defined distances.
- Use 0° to 90° for the rise (add 60mm to the radius),
- For the dwell from 90° to 180°, maintain the same radius,
- For the fall from 180° to 360°, decrease back to the original radius.
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Identify points on the profile: There should be distinct points noted to indicate changes in the profile shape, particularly at the peaks from rising and falling segments, ensuring that each segment reflects the displacement accurately.
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Draw the cam profile: Using smooth curves and lines, transition through the angles marked to create the final cam profile representation. Ensure smooth joining of points and proper depiction of the cam's rising and falling motion.