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C-4. A cam, as shown, is often used as part of a sewing machine - Leaving Cert DCG - Question C-4 - 2021
Question C-4
C-4. A cam, as shown, is often used as part of a sewing machine. (a) Draw the displacement diagram for a cam which imparts the following motion to an inline knife e... show full transcript
Worked Solution & Example Answer:C-4. A cam, as shown, is often used as part of a sewing machine - Leaving Cert DCG - Question C-4 - 2021
Step 1
Draw the displacement diagram
Answer
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Divide the circle into 360°: Since the motion is described in terms of angular intervals, a complete circle of 360° is required.
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Set the scale: Use a distance of 15mm to represent each 30° interval in the diagram.
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0° to 90°: Rise 60mm: From 0° to 90°, draw a straight line rising up to 60mm using uniform velocity.
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90° to 180°: Dwell: From 90° to 180°, draw a horizontal line to indicate that the follower remains at this height without movement.
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180° to 360°: Fall 60mm: From 180° to 360°, draw a curve indicating a fall of 60mm with uniform acceleration and retardation. This can be represented by a gradual curve that falls back to the original height.
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Complete the displacement diagram: Ensure that all parts are clearly marked with appropriate angles and heights to complete the full diagram.
Step 2
Locate Points A, B, and C
Answer
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Set up line diagram (O, A, B & C): Draw point O as the center from which crank OA rotates.
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Dimension points: Mark point A at the end of the crank OA and indicate the fixed position of point O.
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Position point B: Draw rod AC connected to point A and mark point B on this rod, considering the length of the rod AC.
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Draw point C: Mark point C on the vertical line where it is supposed to move as the crank rotates, ensuring its path is clear.
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Indicate rotation directions: Clearly add arrows showing that crank OA rotates in a clockwise direction.
Step 3
Draw the locus for point B
Answer
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Trace the movement of point B: As crank OA rotates, observe and map the movement of point B based on the angle of rotation.
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Plot positions for multiple angles: Begin at 0° and mark the position of point B at various intervals (30°, 60°, 90°, etc.), noting how it moves relative to A and O.
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Connect the plotted points: Draw smooth curves or lines connecting these plot points to effectively depict the locus of point B’s movement as the crank rotates fully.
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Label the locus clearly: Ensure the locus is clearly labeled and distinct from other lines in the diagram for clarity.