Internal Geneva Mechanism

INTERNAL GENEVA MECHANISM

AIM:

1. To create the 3D model of the internal Geneva mechanism.
2. To create 3D models for driver and driven wheels.
3. To Perform motion analysis by rotating the driver wheel at 10rpm and 20rpm.
4. To obtain the following plots:

• To enable the precision contact option and study its effect on the plots.
• To plot the contact force between both driver and driven wheels.
• To plot the angular velocity and angular displacement of the wheels.

INTRODUCTION:

• The Geneva drive or Maltese cross is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion.
• The rotating wheel is usually equipped with a pin that reaches into a slot located in the other wheel (driven wheel) that advances it by one step at a time.
• The drive wheel also has an elevated circular blocking disc that "locks" the rotating driven wheel in position between steps.

THEORY:

An internal Geneva drive is a variant of the design. The axis of the drive wheel of the internal drive can have a bearing only on one side. The angle by which the drive wheel has to rotate to effect one step rotation of the driven wheel is always smaller than 180° in an external Geneva drive and always greater than 180° in an internal one, where the switch time is, therefore, greater than the time the driven wheel stands still.

PROCEDURE:

2D CAD drawings to create the 3D model of the internal Geneva mechanism

1. 2D Diagram of Driven wheel with the following dimensions.

Steps:

1. Open Solidworks and start a new part.
2. Draw three circles with the above-mentioned dimension.
3. Draw an imaginary line between two circles.
4. Select the line and create offset entities by selecting cap ends and bidirectional option with a dimension of 20mm.
5. Now create the circular sketch pattern of four slots as in the picture.
6. Trim the unwanted sketch entities using the power trim command.
7. Use sketch fillet command of radius 50mm in between the four slots and the circle.
8. Now extrude the given sketch as 40mm and direction as blind.
9. Now save this as a geneva-driven wheel part.

1. 2D Diagram of Driver wheel with the following dimensions.

Steps:

1. Now use geneva driven wheel sketch as a reference to make our geneva driving wheel as shown above.
2. Create new sketch and enter the front plane.
3. Select a centerline command and draw a line in between two slots from the center of the driven wheel and make an angle of 45 deg
4. Draw a perimeter circle using both slot centerline and tangent to each other.
5. Now select a point and intersect between centerline, perimeter circle, and origin midpoint.
6. Now take intersection point as reference and draw a circle of 40mm diameter and draw a driving wheel circle of 420mm at a distance of 160mm from the point of intersection to the center of the driving wheel.
7. Now exit from the current sketch and hide the driven wheel sketch.
8. Extrude the given sketch of 20mm and point circle to 40mm from the above surface.
9. Save the part as a geneva-drive wheel mechanism.

ASSEMBLING OF GENEVA DRIVER AND DRIVEN PART

Steps:

1. Select Assembly part and click OK
2. Insert both the geneva driver and the driven part.
3. Use mate command to constraint the axis of the driver and driven mechanism.
4. Thus the mechanism mated as shown in the above figure.

MOTION ANALYSIS OF INTERNAL GENEVA MECHANISM

CONTACT FORCE BETWEEN INTERNAL GENEVA MECHANISM

• 25 frames per second for 10RPM

• 60 frames per second of 10 RPM without precise contact

• 60 frames per second for 10RPM with precise contact

• 120 frames per second for 20 RPM without precise contact

• 120 frames per second for 20 RPM with precise contact

ANGULAR DISPLACEMENT OF DRIVEN WHEEL (FOR 20 RPM)

ANGULAR VELOCITY OF DRIVER WHEEL (FOR 20 RPM)

RESULTS AND PLOTS

PLOTS OF CONTACT FORCES OF INTERNAL GENEVA MECHANISM

• 25 frames per second for 10 RPM

• 60 frames per second for 10 RPM without precise contact

• 60 frames per second for 10 RPM with precise contact

• 120 frames per second for 20 RPM without precise contact

• 120 frames per second for 20 RPM with precise contact

ANGULAR VELOCITY OF DRIVER WHEEL (FOR 20 RPM)

ANGULAR VELOCITY OF DISPLACEMENT WHEEL (FOR 20 RPM)

ANIMATION OF INTERNAL GENEVA MECHANISM

https://youtu.be/zdMG93G2YEA