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Power Transmission Systems: Calculations and Key Systems

## Gear Train and Joint Options

You are working for a company who build power transmission systems. An opportunity to take on a team lead role has become available.  In order to prepare for the interview your manager has suggested you build a small portfolio of evidence showing your capacity to perform calculations relating to power transmission and that you have an understanding of the key systems your company uses.

A) Your company are working on a design for a new punch press. The press contains a compound gear train to alter the speed and torque supplied by a motor to make it suitable for powering the equipment.

Calculate:

• The output speed in rev/min and the direction.
• The output power
• The holding Torque.

B) The gear box is mounted to an output shaft which is offset to the equipment it must drive. In the past the company have used 2 different types of couplings for this sort of system: A Hook’s Joint or a Constant Velocity joint. You have been asked to review the different joint options.

• Describe how the Hook’s works and analyse the limitations of Hook’s joint when used to transfer constant angular velocity in a mechanism.
• Explain how 2 Hook’s joints can be used to create a constant a velocity coupling and the conditions required to ensure a constant velocity ratio between the input and output shafts.
• Describe how the Constant Velocity joint works and explain the design features that allow constant velocity transfer.
• Explain why this is necessary to have constant velocity transfer for some applications.

Some reference to the joints operation and transfer speeds should be included with suitable diagrams where necessary.

C) A flywheel is a mounted to the output shaft in the punch press, the purpose of a fly wheel is to store rotational mechanical energy.

• Describe how the flywheel stores the energy your answer must include reference to angular momentum, torque and inertia.
• Research and describe the operation of one other device that stores mechanical energy.

D) Mechanical power transmission failure is a concern with any design, to demonstrate your awareness of this issue find an example of a documented case of a mechanical power transmission system that has failed.

• Describe the mode of failure
• Describe the steps taken to correct the problem /changes made to the design.

Ensure you reference the documented case using the Harvard system.

Your company have been awarded some contracts where power must be transmitted via screw jacks and lead screws.  Complete the below calculations to demonstrate your ability to lead a group of workers designing systems of this nature.

An acro-prop support is being used to raise a load within the punch press; the vertical force required from the acro-prop is 4,500N.

The screw has a pitch of 7mm and a diameter of 70mm.

The bar used to raise the load is 350mm long and the coefficient of friction (µ) is 0.2

From this information calculate:

• The efficiency of the system.
• The effort required to raise the load.

The lead screw must move a load with a force of 1200N

The lead screw has a pitch of 4mm and a diameter of 40mm.

The coefficient of friction for the screw is  0.25.

• Determine the efficiency of the lead screw.
• The torque required to move the load.

Calculate the operating efficiency of lead screws and screw jacks.

Explain the conditions required for a constant velocity ratio between two joined shafts.

Examine devices which function to store mechanical energy in their operation.

Examine the cause of a documented case of mechanical power transmission failure and the steps taken to correct the problem and rectify any design faults.