Snipper Research Articles

Study on Dynamic Behaviour of Grass Trimmer Using Finite Element Analysis

Nowadays, research on dynamic behavior of structural components is becoming one of the important parts in the design process for any mechanical system. In order to determine the dynamic behavior of a vibrating structure, measurements of the dynamic properties of structure are essential. Free vibration analysis is one of the approaches that apply the finite element method in determining the structure modes of vibration. Each mode is defined by its natural frequency and mode shape. In this paper, the free vibration analysis of grass trimmer was performed using commercial finite element software, such as Ansys®. The importance of determining these vibration characteristics are crucial as grass trimmer is a common machine that exposed to the dynamic and static forces coming from the engine and rotating blade. A long term exposure of grass trimmer's operator may or potentially suffering a risk of hand arm vibration syndrome. The preliminary results of free vibration analysis demonstrated that the grass trimmer experienced a global first bending mode for 1st natural frequency, a global second bending mode for 2nd natural frequency, a local first torsion mode for third natural frequency, and a combination of global and local bending mode for 4th natural frequency. Later, the analyses were further carried out on the modification of the grass trimmer.

Mowing for biodiversity: grass trimmer and knife mower perform equally well

Mowing of semi-natural grasslands is an important management method to maintain the conservation value and species-richness of this habitat. Mowing using cutting instruments, e.g. sickle bar mowers, is thought to be superior by practitioners compared with other mechanical instruments that tears off the plant material, e.g. grass trimmers. However, almost no studies exist that supports this assumption. We analysed a 12-year field trial in a semi-natural grassland in south-eastern Sweden, with the aim of determining which mowing technique best maintains the conservation value of semi-natural grasslands. Two mowing techniques were compared: mowing using a hand-pushed sickle bar mower (a type of knife mower), or mowing using a grass trimmer at a 5-cm or 0-cm cutting height. The odds that a recorded species belongs to a group of indicator species were calculated for sample plots, and odds ratios were calculated contrasting treatments. Three types of indicator species classification systems were used: (i) indicators of management for species richness, (ii) indicators of excess nitrogen and (iii) indicators of lack of management. The odds ratios were calculated for years 1–5, 7 and 12 of the trial. In addition, Principal Response Curve analysis was performed to analyse the change in vegetation composition over time and ANOVA for plant species richness in plots. The results showed that over time there were no differences in the odds of finding indicators of any of the three types, for any of the mowing techniques. Furthermore, there were no apparent change in vegetation composition and only a small effect on richness. These results suggest that mowing using a sickle bar mower or a grass trimmer had the same effect on the floristic composition of grasslands, and both techniques can be recommended for use in semi-natural grasslands.

Design Management for Sustainability: An integrated approach for the development of sustainable products

The need for sustainable products has sensibly increased in recent years. Even though well-established tools have been developed to help designers in facing with environmental problems (i.e., ecodesign), a more user-centred approach which follows design for sustainability issues has not been proposed yet. On these considerations, a specific design for sustainability procedure, named Design Management for Sustainability (DMS), is outlined and tested through its application to the re-design of an engine driven grass trimmer. The proposed framework resulted in an effective design management tool, allowing us to perform design activities in compliance with the goal of sustainability.

Development of Machines for Flaming Weed Control on Hard Surfaces

<abstract> <bold><sc>Abstract. </sc></bold>Weed control is a major issue not only in agriculture but also on hard surfaces in urban and suburban contexts. Weeds can cause serious damage to urban structures and are often considered as a sign of neglect. Moreover, citizens are becoming increasingly aware of environmental pollution and its potential risks for their health. Flaming represents a concrete alternative to herbicide applications on hard urban surfaces. Flaming can also be a good alternative to mechanical means (e.g., string trimmers) which can seriously damage surfaces because they are too intense and in any case are often not effective. The aim of this work is to describe LPG fed flaming machines designed and built at the University of Pisa, Italy. Liquefied Petroleum Gas (LPG) is a flammable mixture of hydrocarbon gases–propane and butane. Four different machines were developed and tested in four different urban and sub-urban contexts. A small backpack flamer equipped with a manual lance was tested on a stonewall, a trolley machine with a manual lance was used to clean the base of ornamental trees, a self-propelled machine was tested in a railway station, and a mounted machine was used in a suburban cycle way. Flaming was compared to the ordinary weed control systems such as using herbicides or mowing. The results showed that flaming can be both less expensive and more effective (on average less that 1 € m^-2 year^-1 maintaining weed cover below 5% to 6%) than the ordinary treatments in urban areas. Flaming was more effective than mowing in the suburban area but much more expensive, thus an integrated approach would be advisable in this context. Future research should be devoted to improving the efficiency of the treatment, using for example, new burners with secondary air and precision agriculture technologies.

Development of a Semi-Automated Tobacco Stripping Machine Utilizing String Trimmers

<abstract><title><italic>Abstract.</italic></title> Conventional stripping of burley tobacco is labor intensive and typically requires 50 to 75 worker hours per acre (wkr•h/acre). The goal of the project was to reduce labor by optimizing leaf removal by string trimmer heads using combinations of strings lengths and motor speeds. In tests conducted on a single grade, all leaves outside the grade were removed by hand. Plants were run through the machine for string lengths of 13, 18, and 23 cm (5, 7, and 9 in.) and associated motor speeds which were monitored and recorded. Stripping efficiencies were calculated for each plant and collectively for each set of four plants. The machine was then tested for three grade stripping efficiency. Particle size analysis tests were run to determine potential losses due to leaf shredding. Efficiencies for single grade testing ranged from 93% to 96% for optimal string length and speed combinations. Stripping three grades by machine resulted in an average of 97% efficiency. Potential losses due to shredding accounted for 5.6% of the total weight mechanically removed. It is believed that this stripping concept, implemented on a full scale four grade basis, could result in savings of at least 45 wkr•h/ha (18 wkr•h/acre).

Nodal control of grass trimmer handle vibration

Imposing node technique is applied to the grass trimmer shaft in order to achieve very low vibration (node) at the handle location. The optimum tuning frequencies of the two tuned vibration absorbers (TVAs) attached at 0.74L and 0.85L along the shaft of the grass trimmer are determined using the imposing node technique. Transverse deflection, experimental modal analysis and operating deflection shape analysis of the grass trimmer were carried out, and the results indicated that nearly zero deflection (node) was induced at the position very close the loop handle location. Moreover, the vibration along the segment of the shaft (0.70L–0.94L) was also found to have relatively small amplitude. The TVAs were found to have best performance with 71% reduction on the frequency weighted rms acceleration at the loop handle and 72% for the rear handle. The results from the experimental modal analysis and operating deflection shape revealed that the presence of the two TVAs has successfully reduced the large deformations of the loop and rear handle where the node was shifted nearer to the handle location. The effects of TVAs were also evaluated during the field test involving grass trimming operation and subjective rating. The results indicated that average reduction of frequency-weighted rms acceleration was by 25%, 69%, 17%, 58% in Xh-, Yh-, Zh- axes and vibration total value respectively during the cutting operation. From the field test, subjective rating of vibration perception consistently rate better for the controlled grass trimmer. Relevance to industryLarge numbers of workers are employed to perform grass trimming job in maintenance of parks and areas with undergrowth. This paper presents the imposing node technique to control handle vibration to the lowest value.

Opportunities to Develop Programs and Engage Amish Youth in Safety Education

Understanding and designing appropriate educational youth safety programs for the Amish requires an appreciation of their history, their distinctiveness in an American society built on economic, social and cultural change, and how the Amish themselves have changed over the years. The qualitative research study highlighted in this paper sought to determine culturally and age-appropriate curricula useful to community educators interested in youth safety programs for Amish and other conservative Anabaptist groups. Researchers identified rural safety topics of interest to Amish families to include lawn mowers, string trimmers, chemicals, water, livestock, confined spaces, tractors and skid loaders. Parents regularly involved children in daily farm chores, where they made assignments based on the child’s physical development, maturity, interest in the task, and birth-order. Findings suggest opportunities for cooperative extension professionals to develop and engage Amish children in safety education programs.

Nonchemical and Herbicide Treatments for Management of Japanese Stiltgrass (Microstegium vimineum)

AbstractJapanese stiltgrass, an annual grass species native to eastern Asia, has become a serious invasive-plant problem in the eastern United States. We compared the efficacy of herbicides and nonchemical options found effective for controlling stiltgrass in earlier studies, with organic herbicides and herbicides used at reduced rates in a wooded floodplain along the lower Connecticut River. We compared the effect of 2 yr of conventional and alternative treatments on cover of other nonnative and native species. Four blocks of 18 plots (3 by 4 m [9.8 by 13.1 ft]) were established in May 2008. Treatments included directed heating with a propane torch (June, July), hand-pulling (July), mowing with a string trimmer (July, August), foliar applications of household vinegar [5% acetic acid] (June, July) and the herbicides imazapic (June), pelargonic acid (June, July), and pelargonic acid plus pendimethalin (June). The following herbicides were applied at labeled doses and at one-fourth labeled doses: fenoxaprop-p-ethyl (July), glufosinate (August), and glyphosate (August). Stiltgrass cover and height were evaluated periodically, and plant samples were collected in autumn of 2008 and 2009 to determine the number of viable seeds produced. Final evaluations were conducted in June 2010 after 2 yr of treatment. Stiltgrass cover averaged 88% on untreated plots in fall. All treatments reduced stiltgrass cover and seed production. The least-effective treatments were hand-pulling, pelargonic acid, and vinegar in July. Direct heating, mowing, and vinegar in June reduced seed production by more than 90%. All treatments containing imazapic, pelargonic acid plus pendimethalin, fenoxaprop-p-ethyl, glufosinate, and glyphosate completely prevented stiltgrass seed production in the second year of treatment. Effective control of stiltgrass can be achieved during a 2-yr period with a variety of herbicides, including herbicides at one-fourth of the labeled dose, and through nonchemical treatments.

Identifying Culturally and Age Appropriate Farm Safety Curricula for Amish and Other Conservative Anabaptist Youth

In conservative Anabaptist families, especially the Amish, children play many vital roles; this includes participation in daily living chores as well as occupationally related tasks. The goal of this qualitative study was to determine a culturally and age appropriate farm safety curriculum useful for the children of Amish and other conservative Anabaptist groups. The top areas of concern identified were lawnmowers and string trimmers, chemicals, water, livestock, confined spaces, tractors, and skid loaders. Amish children were reported to perform farm chores at a young age. Through this study, researchers did not find a strong tendency for parents to assign chores based on age or gender; rather, these assignments were based on the child's physical development, maturity, interest in the task, and birth order. The findings of this study hold up the need for additional agricultural safety curricula targeted toward children of these church groups for a broad range of ages and on a variety of farm topics.

Commelina diffusaPopulation Dynamics in Banana and Ruderal Habitats under Mechanical and Herbicide Management Regimes

Commelina diffusais a colonising species of banana orchard habitats in St. Vincent in the Windward Islands of the Caribbean. In the present study, the population dynamics ofC. diffusawere investigated in response to mechanical weed management with either a rotary string trimmer or glufosinate in ruderal and banana habitats. The study focused on density and size distribution of the weed over time and their response to two weed management strategies. The population dynamics ofC. diffusadiffered between the two habitats. Seedling establishment appeared to be an important factor influencing the dynamics ofC. diffusain banana orchards as there was little recruitment of seeds with less flower production compared with ruderal habitats where plants produced more flowers. Plants ofC. diffusain the banana orchard habitat had a longer growth cycle. In the banana orchard habitat, theC. diffusapopulation was greater and the plants were shorter with mechanical management than in areas treated with glufosinate. The results suggest that it is possible to manipulate the dynamics ofC. diffusain banana orchards as there is less chance of seed recruitment. Further research is necessary to refine an IPM approach for the management ofC. diffusa.

Predictive factors and outcomes of posterior segment intraocular foreign bodies

To identify the predictive factors for anatomical and visual outcomes in posterior segment intraocular foreign body (IOFB) patients managed by pars plana vitrectomy (PPV). A retrospective chart review was performed for 77 patients, who had PPV for IOFBs removal between January 2001 and July 2007. Univariate and multivariate analyses were conducted to evaluate the predictive factors. The mean age of the patients was 33.4 years. The nature of IOFBs was mainly metal, with injuries most commonly caused by an electric grass trimmer. The mean time interval between injury and IOFBs removal was 30.7 days. The mean preoperative visual acuity (VA) was 1.82 logarithm of the minimal angle of resolution (logMAR), and mean final was VA 1.10 logMAR. From multivariate analysis, good visual outcome was correlated with the corneoscleral entry site, and poor visual outcome was correlated with the presence of relative afferent pupillary defect. In noncombat IOFBs, most cases were work-related. Delayed IOFBs removal was acceptable when primary wounds were repaired appropriately and extensive antibiotics administered. Even though advancement in vitreoretinal surgery can reduce the frequency of blindness, further promotion and education on eye protection during work are needed.

Tuned vibration absorber for suppression of hand-arm vibration in electric grass trimmer

Prolonged use of electric grass trimmer exposes the user to the risk of hand-arm vibration syndrome. A simple approach for the suppression of hand-arm vibration in electric grass trimmer is presented. The proposed system is a tuned vibration absorber (TVA). Modal analysis and operating deflection shape analysis of the electric grass trimmer were carried out and a TVA was designed and fabricated for testing. The results indicated that minimum vibration level was related to the position of the TVA on the shaft of electric grass trimmer. The TVA was found to have best performance with 95% reduction on the acceleration level at position 0.025L. The results from modal analysis and operating deflection shape revealed that the presence of TVA has successfully reduced the large deformations of the handle where the node was shifted nearer to the handle location. The effect of TVA was also evaluated during field test involving grass trimming operation and subjective rating. The results indicated that average reduction of frequency-weighted rms acceleration in the Z h- axis was 84% and 72% in X h- axis for the cutting operation. For the no cutting operation, the reduction is 82% in Z h- axis and 67% in X h- axis. The presence of TVA in the electric grass trimmer has amplified the vibration level in Y h- axis by 19% (no cutting) and 21% (cutting). From the field test, subjective rating of vibration perception consistently rate better for controlled electric grass trimmer. Relevance to industry The tuned vibration absorber when installed to the electric grass trimmer attenuated the vibration total value by 67%. This significantly reduces the risk of hand-arm vibration syndrome.

The design and development of suspended handles for reducing hand-arm vibration in petrol driven grass trimmer

The portable petrol driven grass trimmer is identified as a type of machine whose operator can be subjected to large magnitude of hand-arm vibration. These vibrations can cause complex vascular, neurological and musculoskeletal disorder, collectively named as hand-arm vibration syndrome. The vibration total level on the handle of grass trimmer of 11.30 m/s 2 was measured, and it has reached the exposure limit value of 5.0 m/s 2 for daily vibration exposure A(8). New suspended handles were designed to reduce the vibration level. Three different prototype handles with rubber mounts were designed. Handles were made of different materials, and the distance of rubber mounts were varied. From the study, it was observed that not all the handles with rubber mounts were effective in reducing hand-arm vibration. The reduction of vibration depended on the handle material and distance installed between rubber mount and vibration transmissibility of handle-isolation system. Subjective ratings of perception of vibration were measured, and the results indicated that operators were not fully aware of the level of vibration. A prototype handle that is made of heavier material results in the lowest hand-arm vibration of 2.69 m/s 2. The new handle has significantly reduced the vibration total value by 76% compare with the existing commercial handle. Relevance to industry Large numbers of workers are employed to perform grass trimming job in many developing countries. This paper presents the effect of handle types (commercial and prototype) on the commonly used grass trimmer.

Optimization of the operating parameters of a grass trimming machine

Hand–arm vibration syndrome (HAVS) is very common among the workers operating power tools and doing similar nature of work for long hours. Grass trimming is one of the operations that involves use of vibrating cutter, and results in hand–arm vibration among workers. In this study, the influence of several operating parameters (length of nylon cutting thread, engine speed and handle material) is investigated in terms of HAV. Data are analyzed via orthogonal array, main effect, signal-to-noise (S/N) ratio, and analysis of variance to determine the appropriate operating parameter levels to minimize HAV. Operating parameters under investigation are found to be influential in controlling HAV generation during grass trimming operation. Experiments are carried out for measuring hand–arm vibration using tri-axial accelerometer conforming the effectiveness of this approach. Results show that 100 mm length of nylon thread, 3000 ± 400 rpm of engine speed and ABS handle material combination results in minimum HAV (HARM) of magnitude 2.76 m/s 2. Through this study not only the optimal operating parameter levels for GTM are obtained, but also the main process parameters that affect the HAV are determined. The optimum HAV obtained through appropriate level selection of operating parameters, significantly reduces the occurrence of HAVS among the grass trimmers.

Evaluation and Optimization of Handle Design Parameters of a Grass Trimming Machine

The grass trimming machine is a widely used agricultural machine for cutting grass by the roadside and in other areas in Malaysia. Hand-arm vibration (HAV) syndrome is very common among workers operating power tools and performing similar work for extended periods. Grass trimming involves the use of a motorized cutter spinning at high speed, resulting in high levels of HAV among its operators. The existing D-shape handle causes HAV-related stress and operational load in operators. This research proposes a new design of a handle of the grass trimming machine. When this new design was compared with the old one, it was found that the new handle resulted in 18% lower HAV. To find the lowest HAV, 3 critical parameters of the new handle (length, angle and material of the cap of the handle) were optimized using the Taguchi quality tool. Appropriately selected parameters of the new handle significantly reduced the occurrence of HAV among grass trimmers.

Optimization of operating parameters for a back-pack type grass trimmer

Hand–arm vibration syndrome (HAVS) is very common among workers operating power tools and performing similar work for extended period of time. Grass trimming involves the use of motorized cutter spinning at high speed, resulting in high levels of hand–arm vibration (HAV) among the machine operators. In this study the influence of handle–hand interaction of a grass trimming machine (GTM) is evaluated based on different hand positions of operator during operation. Besides, several operating parameters (length of nylon cutting thread, engine speed and sway angle) are investigated in terms of HAV. Three handle–hand positions (HHPs) are studied that are generally adopted by the GTM operators during their work. Data are analyzed via orthogonal array, main effect, signal-to-noise (S/N) ratio, and analysis of variance to determine the appropriate operating parameter levels and HHP to minimize HAV. HHPs and operating parameters under investigation are found to be influential in controlling HAV generation during grass trimming operation. Experiments are carried out for measuring hand vibration using a tri-axial accelerometer conforming the effectiveness of this approach. It is shown that among the three HHPs considered in this study, optimum result in terms of HAV is 2.42 m/s 2. Moreover results show that 170 mm length of nylon thread, 3000±400 rpm of engine speed and 45° of sway angle combination results in minimum HAV (HARM) of magnitude 2.42 m/s 2. Through this study not only the optimal operating parameter levels for GTM are obtained, but also the main process parameters that affect the HAV are determined. The optimum HAV obtained through appropriate selection of HHP and operating parameters, significantly reduces the occurrence of HAVS among the grass trimmers. Relevance to industry The paper discusses the evaluation of HAV for GTM, which is widely used in Malaysia for grass trimming operation especially by the side of highways. A large number of workers are employed by the highways authority for this purpose. GTM used for this purpose should have as low HAV as possible so as to avoid damage in terms of HAVS.

Carbonaceous species emitted from handheld two-stroke engines

Small, handheld two-stroke engines used for lawn and garden work (e.g., string trimmers, leaf blowers, etc.) can emit a variety of potentially toxic carbonaceous air pollutants. Yet, the emissions effluents from these machines go largely uncharacterized, constraining the proper development of human exposure estimates, emissions inventories, and climate and air quality models. This study samples and evaluates chemical pollutant emissions from the dynamometer testing of six small, handheld spark-ignition engines—model years 1998–2002. Four oil–gas blends were tested in each engine in duplicate. Emissions of carbon dioxide, carbon monoxide, and gas-phase hydrocarbons were predominant, and the PM emitted was organic matter primarily. An ANOVA model determined that engine type and control tier contributed significantly to emissions variations across all identified compound classes; whereas fuel blend was an insignificant variable accounting for <5% of the observed variation in emissions. Though emissions rates from small engines were generally intermediate in magnitude compared with other gasoline-powered engines, numerous compounds traditionally viewed as motor vehicle markers are also present in small engine emissions in similar relative proportions. Given that small, handheld two-stroke engines used for lawn and garden work account for 5–10% of total US emissions of CO, CO 2, NO x , HC, and PM 2.5, source apportionment models and human exposure studies need to consider the effect of these small engines on ambient concentrations in air polluted environments.

Absence of14C in PM2.5 Emissions from Gasohol Combustion in Small Engines

PM2.5 combustion emissions from small engines (string trimmer and chainsaw) using gasoline containing biogenic ethanol were collected and analyzed for their 14 C content. The sampling methodology was designed to minimize potential bias from organic artifact effects. The 14 C in the PM2.5 emissions was found to be drastically smaller (approximately a factor of 40) than the 14 C amounts measured in the fuels. This suggests that the current method of using 14 C measurements on ambient aerosol to estimate the contribution from fossil fuel combustion will be little affected by increased use of ethanol-containing gasoline.

Air contaminant exposures during the operation of lawn and garden equipment

The US Environmental Protection Agency (EPA) initiated the Small Engine Exposure Study (SEES) to evaluate potential exposures among users of small, gasoline-powered, non-road spark-ignition (SI) lawn and garden engines. Equipment tested included riding tractors, walk-behind lawn mowers, string trimmers, and chainsaws. Personal and background air quality measurements were collected on equipment operators for carbon monoxide (CO), particulate matter <or=2.5 microm in aerodynamic diameter (PM(2.5)), volatile organic compounds (VOCs), and aldehydes. PM(2.5) measurements included continuous and integrated mass, elemental and organic carbon (EC/OC), and trace metals. Aldehyde measurements included speciation for formaldehyde and acetaldehyde. The results demonstrated that equipment operators can experience elevated exposures to CO, PM(2.5) and air toxics while operating these engines. Ten-second average CO personal exposures spanned over two orders of magnitude, with short-term concentrations exceeding 120 p.p.m. for some engine applications tested. PM(2.5) concentrations averaged over each engine test period also spanned two orders of magnitude. The results also suggest that health standards, such as the CO and PM(2.5) National Ambient Air Quality Standards (NAAQS), may be exceeded for certain equipment types under certain operating scenarios. Aldehyde measurements suggested exposures from primary engine emissions that exceed typical ambient concentrations, but do not exceed occupational health standards. Continuous exposure measurements illustrated the important role of the operator's activity and environmental conditions in affecting exposure levels.

Growth and Yield Response to Simulated Hail Damage in Guar

Hail damage can result in substantial economic loss to annual spring and summer crops. Crop insurance guidelines to assess hail damage on major crops are readily available to adjusters. However, research and guidelines to assess hail damage on minor crops is lacking and may limit their expansion. A dryland field study with guar [Cyamopsis tetragonoloba (L.) Taub.] was designed to determine the effect of simulated hail damage at two growth stages and three levels of defoliation on plant regrowth and bean yield. Experiments were conducted on a Miles fine sandy loam (fine‐loamy, mixed, superactive, thermic Typic Paleustalfs) near Vernon, TX, from 2001 through 2003. A commercial grass trimmer was used to simulate hail damage by flailing plants to targeted defoliations levels of 33, 66, and 90% at 6 and 12 wk after emergence (WAE). Both final plant height and yield were reduced to a greater extent when plants were damaged at 12 WAE (grain‐fill period) than at 6 WAE (early flowering). Regression analysis from data combined over years showed that guar yields were reduced 50% with a 66% defoliation level at 6 WAE, but required only 42% defoliation to reduce yield levels 50% with late‐season defoliation. This is the first report of using a grass trimmer to simulate hail damage by shredding plant material rather than manually removing plants and plant parts. Results from this study also provide a basis for producers and insurance adjusters to quantify and estimate economic losses in guar due to hail damage at two growth stages.