Design and Finite Element Analysis of a Manually Operated Lawn Mower

Abstract

The preservation of the environment is important as it supports our very existence and this creates the need to develop products or machines which do not pollute the environment, but help preserve it. There exist two basic types of lawn mowers:  the reel and the rotary. The reel mower is manually operated, cuts at a very slow rate, making it user unfriendly. Furthermore, reel type mowers are usually expensive and difficult to maintain. The initial and operation cost of the rotary mower are high because it employs an internal combustion engine or an electric motor in its operation. Additionally, the rotary mower engine is very noisy, and releases harmful gases into the atmosphere, thereby having negative effects on the environment. Consequently, a new design of lawn mower which is environmentally friendly and affordable is considered in this work.  At the heart of this design is a worm gear set which converts the forward motion of wheels to a horizontal rotation of blades. The blades rotate at 259 rpm and move relative to the stationary blades, causing a scissoring action against the grass, thus enabling a clean cut. For a push of 502 N, a shearing force of 46 N is generated at the tip of the blades which is used for the scissoring action. A finite element analysis was performed on the cutting blades assembly to examine the effectiveness of the design. The results showed that the scissoring effect of the shearing blades was efficient, as they were able to smoothly cut through a pair of cylindrical grass products.