Evaluation of vibration at the handles tractor

 

    Summary describes the problems caused by vibration white finger, analyze issues related to the evaluation of the vibration, the magnitude of proposed evaluation recommendations.

 

    [Abstract] The paper describes white finger problem caused by vibration, analyses problems

 

    related to bibration evaluation, makes a suggestion on evaluation index.

 

    Key words: weighted acceleration vibration at the handles

 

    National tractor factory nearly 100 tractor holdings reached more than 500 million units, is the world's largest country ownership, hair rhinoceros in the rural economy plays a huge role. However, tractor handlebar vibration greater endanger the driver's health. It is necessary to study how to quickly evaluate and limit tractor handlebar vibration, to ensure that the driver's health.

 

    One, vibration disease

 

    When operating tractor, like the use of other handheld vibrating tools, vibration acts on manpower, it will cause to peripheral circulatory disturbance based diseases, called local vibration disease. More in the upper part of the onset of the end of the finger showed typical white, known as the "white finger." English called VWF (Vibration-indueed White fincer), meaning very clear, that is caused by the vibration white finger. White is a very complicated means elephant, the main mechanism is in the case of prolonged exposure to vibration, hand and finger to smooth muscle contraction, thereby reducing the flow of blood flow to the hands and fingers, the fingers white, resulting in pain, numbness, chills, stiff, swollen, weakness and other local symptoms. May also appear headache, tinnitus, insomnia, joint pain and other systemic symptoms. Especially in cold climates use vibrating tools, more prone to such symptoms.

 

    Many hand-held vibrating tools, such as picks, hand grinders, pneumatic wrenches, pneumatic rivet gun. Hand operated mechanical vibrations, such as walking tractor, with its vibration disease hazards will be ignored. For this reason, many countries have carried out expert research in this area. For example: It has been the use of pneumatic drills (picks) and hand grinders and micro-climates in the same work, but who do not suffer from a comparison of vibration inspection; was found suffering from vibration vibration than people who do not suffer from its Hand skin blood flow decreased by 38% -67%.

 

One of the consequences of blood flow reduction is to reduce the temperature of the skin. Some researchers have actually made a determination, with two groups, one group is set by the vibration, vibration group, another group from the beginning, by the vibration of the hand set low temperature, and then the two human hands into 45 ℃ water heating lOmin, the hand of the two groups of people close to the same temperature, followed by gradual cooling. The results, set by the hand vibration about 2 ℃ low temperature, has been to return to room temperature, by the vibration of the hand set is still relatively low temperature, see Figure 1. Most people do not because of white finger caused debilitating health, but it may cause finger necrosis.

 

 Second, the evaluation of local vibration

 

    Find the country for local vibration-induced vibration disease given attention, the Ministry of Health as early as 1985 that promulgated a national standard GB4869-85 "occupational vibration disease diagnostic criteria and principles." Standard for occupational exposure to local vibration vibration occurs at different levels of three disorders: Observe the object level, mild vibration disease stage and severe vibration disease stage, and the corresponding diagnostic criteria and treatment principles. On the observed object, you should review the first 1 to 2 years. For mild, should be removed from the job and vibration appropriate treatment. While severe vibration must be removed from the job, active treatment, to reduce the disease before for other light work. This indicates that vibration disease may endanger the health and lead to a loss of ability to work.

 

    In order to evaluate local vibration and restrictions, many foreign countries have made a lot of methods and guidelines, but these guidelines varies widely between, due to lack of sufficient basis for medicine and physiology, is difficult to determine exactly which one is best right, which one should be used. International Organization for Standardization (ISO) in 1977 developed a set of evaluation guidelines --lSO/DIS5349 "human exposure to hand-transmitted vibration - Measurement and Evaluation Guide" (Figure 2), this guide octave and 1/3 octave history analysis of each band to limit vibration levels, taking into account the time and vibration by the vibration interval conditions and other factors. After several years of use and research, and in January 1983 proposed amendments to the draft, the number and names are kept in its original, but in the methods of evaluation were large movements (Fig. 3), there are two main : The first is to evaluate the basic point is to hand vibration input energy equal to the energy that would cause the same damage, the draft amendment to the daily energy such as frequency-weighted acceleration 4h as an evaluation of the main parameters. The second is to consider harm to human body vibration group statistical results, rather than the original draft as long as there is a frequency vibration levels exceed the specified limits, shall be deemed not allowed. Figure 3 The relationship between the amount of the following approximate relationship:

 

Questions, different people react differently to the same vibrations, even the same person, at different times, under different circumstances to the same vibration response is not the same, the annual order, gender, physical and psychological status and ambient temperature and humidity other factors will affect the human response to vibration. Therefore, it is difficult to make money with an absolute exact, positive evaluation. Proposed opponents transmitted vibration from the initial evaluation of the problem has been more than 20 years, ISO draft amendment to the evaluation guide for 10 years now, but due to the lack of hand-transmitted vibration is still harmful effects on human sufficient quantitative data have therefore not formed as a formal standard evaluation criteria. Solution to this problem has been evident the complexity and difficulty, however, based on the protection of the health of most people ISO/DIS5349 evaluation guidelines in the current conditions, yet it is ... a more objective and guiding principles. In the evaluation of vibration at the handles on the tractor, using as a basis the draft is more appropriate.

 

Third, the evaluation of vibration at the handles tractor

 

    There has been a national standard GB7927-87 "tractor vibration measurement methods," but to make accurate assessment of the vibration, which must also be relevant conditions and factors more stringent requirements.

 

    1. Measurement state

 

    In the past, people used to the tractor parked, engine operating condition measure vibration called "static measurement," while driving the tractor vibration measurement known as the "dynamic measurement." Because the instrument and other conditions, most have adopted a more simple "static measurement." I.e., non-running state measurements. However, this measurement state can not reflect the actual situation. First, the non-driving state of the handlebar vibration, just by the engine's working process and its working imbalance caused no incentive ground vibrations caused through the wheel, and this is precisely a greater impact low-frequency vibrations. Second, in the non-running state, tractor primarily for pumping, threshing and other fixed-based operation, but this time, no need to hold the tractor tractor driver's hand, it does not exist vibration on the human body. For these two reasons, the measurement of non-driving state of the vibration no practical significance, and the measurement of the state should be traveling.

 

    Tractor driving state of the job types are mainly three kinds, namely plow, cultivator and road transport. Tests showed that in these three kinds of operations, transport operations to the highest handlebar vibration, rotary, followed by plowing the lowest (see Table 1). In China's actual use of the tractor, is precisely the large proportion of transport operations. Therefore, in order to effectively protect the health of tractor shall state on the road to simulate transport test measurements to evaluate more reasonable.

 

    2. Measuring Road

 

    GB7927 - 87. Vibration measurements as specified in the typical rural dirt road or in the standard artificial vibration test runway. But the actual rural dirt road, across very different, even with a dirt road, at different times, for example, through rain, snow, or used after a period of time, will change a lot, poor reproducibility of measurement results, the measurement results poor comparability between each other, so that the quality of product performance appraisal, inspection, evaluation for the purpose of comparing the vibration measurements, the rural dirt road in the actual conduct is clearly inappropriate, but should remain stable in the road conditions, and to represent the rural dirt road on a hard surface, the national standard GB6972-86 "agricultural tractor seat vibration measurement" in the provisions of lOOm standard artificial runway is able to meet this requirement, but also for the international community generally recognized and adopted on behalf of the rural dirt road Standard artificial surface, in which the measurement results on the runway with high repeatability and comparability.

 

    3. Measuring speed

 

    Tests showed that running speed greater impact on financial results of the measurement. For example, the prototype artificial measured on the standard track, the vehicle speed is 10. 9km / h, the weighted acceleration of 10.787In/S2, traveling speed to 11. 8km / h, the weighted acceleration increases to 12. 396m/s2, namely speed 0. 9km / h, the results increases 1.609rri/s2. Tractor transport operations generally have two files, the first transport files mostly in the 15-18km / h, with better conditions for road asphalt, gravel on the job. The second transport files mostly in the 10 ~ 12km / h, poor road conditions for the dirt road. Vibration measurements of the speed appropriate to the second transport files, uniform provisions of 1.2 ± 0. 5km / h, and some may not have 12 tractor with disabilities 0. 5km / h working file, you can by changing the speed of the engine speed will be adjusted this range. In order to ascertain the engine speed changes on measurement results, for the same prototype, first with the V range, the engine full throttle, when the engine speed is 2700r/min, driving speed of 11. Okm / h, measured weighted acceleration to 11. 271m/s2, then Ⅵ files, speed remained at 11. okm / h, then the engine speed to 1 820rlmin, the result is 11. 023m/s2. As can be seen, the engine speed is reduced by about 1/3, and the result is only reduced 0.248m/s2. Thus, the tractor driving speed greater impact on the measurement results, and the results of impact resistance, the engine speed is very small, can be by varying the speed of the engine driving the tractor speed to within a predetermined range.

 

    4. Measuring direction

 

    In the hand-transmitted vibration evaluation, mainly based on z, y, z coordinate direction with the maximum weighted acceleration single direction, the power of the 25 kinds of different tractor models were measured, the results show that, without exception, were the z direction (i.e. the vertical direction) maximum (see Figure 4), thus, in fact, only the z direction can be measured and evaluated accordingly. This simplifies the test, reducing the data processing workload measurement instrument is relatively simple, easy to implement general manufacturing.

 

    5. Evaluation index value

 

    Single direction, frequency-weighted acceleration as an evaluation indicator in determining its value is limited, consider two factors, first of all, should play a role in protecting health; followed by also taking into account the current level of technology of tractor. If you do not consider this, requirements are too stringent, the existing models no one can meet the requirements, it will cause uncertainty about the manufacturer, is likely to cause each other watching, waiting for the phenomenon. If you require too loose, all through, we reach the purpose of protecting the health of the driver, while not conducive to raising the level of tractor technology.

 

    From the above two factors into consideration, it is recommended to continuous driving tractor Four years later, 90% of people do not appear vibration disease, that is, the incidence may be only 10% as the basis. Thus, by the formula listed above can easily calculate the speed of the driver 4h and other energy-weighted not operate continuously throughout the year tractors, therefore, the actual security work experience more than four years.

 

    Looking at the situation from the measure, of which about 25% of the tractor can meet this requirement, and another 30% or so close to this value, a little improvement can be achieved, and that about half of the remaining models need serious work in order to meet the requirements . Such technological advances on the tractor is also a promotion.