Bicycle Power Research and Design Factors

Transcription

1 Bicycle Power Research and Design Factors Background Summary: Human powered machinery is a great way to supply energy to a machine where electricity is not readily available or reliable. In designing the shredder for plastic bottles transformation in third world areas this is an imperative subsystem that needs to be designed very carefully to ensure the safety of the operators and maximum efficiency of the system as a whole. Below is some research conducted to determine what is needed to have a human powered machine. Needed Requirements: In doing some background research into a company called precious plastics it was found that in order to power a machine that was the most effective at shredding PET a low speed high torque motor was needed. The recommended speed of a motor used for a machine of this sorts was 70rpm. In order to transform that into the amount of rotations per second the following Equation was used: 70rpm 60 Sec = rev/sec With this being calculated, in order to have an effective design, the shaft of the shredder holding the blades must rotate about times per second. This can easily be achieved with bicycle or hand crank power. Hand Crank Vs. Bicycle Foot Power: The big question that is raised when talking about human power is which is a more efficient source of human power a hand crank or bicycle power. For bicycle power the following specs were found from mapawatt.com it was found that: Bicycle Power: Average Cycling Power: Watts/hour Average RPM: rpm ( rev/sec) Average Work Expended: kgm/min

2 In terms of a hand crank the energy expended is a bit different. It is heavily dependent on the crank size and the mechanical advantage of the device. However, an average value can be estimated: Average Power: 100 Watts/hour Average RPM: rpm (comfortable) Average Work Expended: J/hour Overall the bicycle can produce more power per hour. Both options are viable for power source but a bicycle will give us more opportunity for power generation to power the shredder. OSHA Standards: OSHA might not have influence in the countries this system is being introduced into, however they are high standards that ensure operator safety. It is important that in the design of this system we look at how to ensure the operators are safe and comfortable in the working environment. OSHA has released the following Engineering Controls suggestions in designing a successful safe system. Engineering Controls (implement physical change to the workplace, which eliminates/reduces the hazard on the job/task) Use a device to lift and reposition heavy objects to limit force exertion Reduce the weight of a load to limit force exertion Reposition a work table to eliminate a long/excessive reach and enable working in neutral postures Use diverging conveyors off a main line so that tasks are less repetitive Install diverters on conveyors to direct materials toward the worker to eliminate excessive leaning or reaching Redesign tools to enable neutral postures While there are no direct policies relating to human powered machinery some major factors that need to be considered in design include seating design and what aspects of design will limit workplace injury. This is the major challenge we need to address in the design of the system. Chair Design OSHA: Hands, wrists, and forearms are straight, in-line and roughly parallel to the floor.

3 Head is level, or bent slightly forward, forward facing, and balanced. Generally it is in-line with the torso. Shoulders are relaxed and upper arms hang normally at the side of the body. Elbows stay in close to the body and are bent between 90 and 120 degrees. Feet are fully supported by the floor or a footrest may be used if the desk height is not adjustable. Back is fully supported with appropriate lumbar support when sitting vertical or leaning back slightly. Thighs and hips are supported by a well-padded seat and generally parallel to the floor. Knees are about the same height as the hips with the feet slightly forward. MSD Disorders OSHA Examples of Musculoskeletal Disorders (MSDs) Carpal tunnel syndrome Tendinitis Rotator cuff injuries (affects the shoulder) Epicondylitis (affects the elbow) Trigger finger Muscle strains and low back injuries Standard Bicycle Dimensions: In order to properly size a bicycle powered machine, it is a good idea to know the dimensions of a typical bicycle to use as a standard to begin the design process. Below are the standard dimensions of a bicycle in millimeters which will aid in the design for seat height, pedal dimensions, and frame height.

4

5 Gear Ratios: Gear ratios will play an important factor in the transformation of mechanical energy to the system. As of right now since the rpm needed by the shredder is the same as the rpm of the human power input, it looks like we can just stick with a 1:1 gear ratio. The challenge faced here is that we need to ensure a person maintains a consistent rpm for the system to function properly. This is the main challenge moving forward with the design Conclusion: In conclusion there are several factors that need to be taken into consideration when designing this subsystem. Moving onto the next phase of design the following components need to be considered and designed to have a successful mode of human power. Comfortable and Ergonomic Seat Frame with adjustable seat height Frame that connects bicycle power mechanism to shredder Gear ratio to transfer energy from bicycle to shaft of shredder Integration of bicycle onto the crank shaft and how the shear pin will interact Handles for operators to hold onto that are in a neutral position and do not require far reach Housing for the chain so it is not exposed to the elements