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Performance of an oscillating subsoiler in breaking a hardpan
Journal of Terramechanics 36 (1999) 117±125
Performance of an oscillating subsoiler in breaking a hardpan E.P. Bandalan a, V.M. Salokhe a,*, C.P. Gupta a, T. Niyamapa b a Asian Institute of Technology, PO Box 4, Klong Luang, Pathumthani 12120, Thailand Faculty of Engineering, Kasetsart University, Khamphaeng Saen Campus, Nakorn Pathom, Thailand
b
Received 4 May 1998; accepted 9 November 1998
Abstract A single shank tractor mounted oscillating subsoiler was developed to break hardpan, common in sugarcane (Saccharum ocinarum) farms especially after harvest when heavy trucks transport the cut canes from the ®eld to the sugar factory. Field experiments were conducted to determine the optimum combination of performance parameters of the subsoiler. Field tests were conducted at frequencies of oscillation of 3.7, 5.67, 7.85, 9.48 and 11.45 Hz; amplitudes of 18, 21, 23.5, 34 and 36.5 mm; and forward speeds of 1.85, 2.20 and 3.42 km hÿ1 at moisture contents close to the lower plastic limit of the clay soil. A reduction in draft but an increase in total power requirement was found for oscillating compared to nonoscillating subsoiler. The draft and power ratios were signi®cantly aected by the forward speed, frequency and amplitude. Their combined interaction, expressed in terms of the velocity ratio (the ratio of peak tool velocity to forward speed), however, had the strongest in¯uence. At the same velocity ratio, the draft reduction and power increase were less at higher amplitude of oscillation. For the ®eld conditions tested, the optimum operation for least energy expenditure was obtained at an amplitude of 36.5 mm, frequency of 9.48 Hz and speed of 2.20 km hÿ1 with a draft ratio of 0.33 and power ratio of only 1.24. It could be concluded that the oscillating subsoiler reduces draft for breaking hardpan, reduces soil compaction and promotes the use of lighter tractors by utilizing tractor power-take-o (p.t.o.) power to achieve higher eciency of power transmission. # 1999 ISTVS. All rights reserved.
1. Introduction Many soils are susceptible to compaction and the formation of impermeable hardpans below the normal tillage depth. Hammond et al. [1] reported that on * Corresponding author. Tel.:+66-5-524-5450; fax:+66-2-524-6200; e-mail: [email protected] 0022-4898/98/$20.00 # 1999 ISTVS. All rights reserved. PII: S002 2-4898(98)0003 5-4
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moist, tilled sandy soil, 2 to 5 cm-thick pans are formed quite easily after a few trips by tillage machines. Hardpans inhibit root penetration and cause drainage problems which result in reduced crop yields. In Thailand, hardpan formations are common in sugarcane ®elds, especially after harvesting when heavy trucks transport the cut cane from the ®eld to the sugar factory. The ®elds are subsoiled annually to break through and shatter these soil layers to improve drainage for the next crop [2]. The utilization of the tractor p.t.o. power for tillage is not common among Thai farmers and subsoiling is done conventionally, thus requiring very high draft and hence tractor ballasting which consequently results in additional compaction. The vibration of soil engaging tools, like blades, tines or shares has been known to reduce the draft force needed to pull the implement. This is highly desirable for high draft implements such as subsoilers. Such draft reduction has been studied and veri®ed by many researchers including Gunn and Tramontini [3], Hendrick and Buchele [4], Larson [5], and Smith et al. [6]. The use of vibration in tillage also produces better soil breakup, although the total power requirement may not be reduced [6,7]. However, for a certain degree of pulverization, the total energy input per unit mass will be smaller compared to non-vibratory tillage since secondary tillage is minimized [5]. With the reduction in draft for soil cutting using vibratory tillage, it is therefore possible to accomplish high draft requirement operations such as subsoiling with relatively lighter tractors and thus soil compaction can be reduced. Gupta and Rajput [8] studied the eect of amplitude and frequency on soil breakup by an oscillating tillage tool in a soil bin experiment. It was observed that the maximum utilization of energy occurs at an oscillation frequency close to natural frequency of soil. At any frequency, soil break-up increased with increase in amplitude. Niyamapa [9] developed a full scale single oscillating subsoiler intended for the use in sugarcane farms in Thailand. Preliminary investigations showed that it may well be adaptable locally under certain operating conditions. This subsoiler utilizes the tractor p.t.o. power which has higher eciency of power transmission as compared to a passive type subsoiler which utilizes drawbar power. The objective of this study was to test the performance of this oscillating subsoiler under actual ®eld conditions and to establish its optimum operating parameters. Speci®cally, the study was conducted to determine the draft and total power required for soil break-up by the vibratory subsoiler at selected amplitudes, frequencies of oscillation, and forward speeds; and determine the combination of amplitude of oscillation, vibration frequency and forward speed for optimum draft and total power requirement. 2. Materials and methods 2.1. Description of the test site The experiments were conducted at the Kasetsart University, Khampaeng Saen Campus, Nakorn Pathom, Thailand. A one hectare sugarcane ®eld (clay soil) which had already been used as aprons for cane carrying trucks was used for ®eld testing.
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It contained clay with a liquid limit of 28%, plastic limit 22%, cohesion 19.15 kPa, adhesion 4.0 kPa and angle of internal friction 31.4 . The average cone index of the ®eld was 1414 kPa over a depth of 60 cm but the soil strength varied within the area. Hence the area was divided into three blocks having cone indices ranging from 1352 to 1984 kPa (average 1669 kPa) for the ®rst block; 996 to 1765 kPa (average 1422 kPa) for the second and 799 to 1675 kPa (average 1150 kPa) for the third block. Soil bulk density was determined at every 150 mm to 600 mm depth. The average densities were 14.6, 15.5, 15.2, 15.3 kN/m3 at depths 0±150 mm, 150±300 mm, 300± 450 mm and 450±600 mm, respectively. Moisture content of the surface soil (0± 150 mm) varied during the test from 8 to 21.2% and that of second layer (150± 300 mm) from 9 to 27%. However, the moisture condition near the average operating depth of 462 mm was relatively constant, varying from 18 to 22%. 2.2. Test machine and instrumentation A schematic of the oscillating subsoiler is shown in Fig. 1. The tine attached at the bottom of the standard was 400 mm long having a cutting edge of 70 mm width and a lift angle of 30 as recommended by Sakai et al. [10]. Oscillation was accomplished through an eccentric shaft connected to the upper end of the share so that it can be moved forward and backward. The amplitude was varied between 18, 21, 23.5, 34 and 36.5 mm by using crank shafts of dierent eccentricities. Power was transmitted to the crank shaft from the tractor p.t.o. through a pair of spiral-bevel gears having
Fig. 1. Schematic diagram of oscillating subsoiler [9].
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a speed reduction of 3.75 and then to a sprocket and chain with a ratio which can be varied depending on the desired frequency and the p.t.o. speed. To minimize forward speed variation, the engine speed was set to give 540 p.t.o. rpm during the test and the frequency was varied by changing sprocket combinations. The desired frequencies of 3.7, 5.67, 7.58, 9.48 and 11.45 Hz were obtained by using the sprocket reductions of 2.25, 1.5, 1.125, 0.9 and 0.75, respectively. Average forward speeds of 1.84, 2.20 and 3.42 km hÿ1 were obtained by selecting dierent gear ratios. The tractor used was a 43-kW KUBOTA model 5500 DT. The instrumentation system included the measurement of forces in the connecting links, torque, rpm, operating depth and angle of inclination of the upper link. For the strain gauge transducers, a six-channel auto-balancing strain ampli®er was used to amplify the signals. All measurements were recorded on a seven channel magnetic tape recorder for further analysis. A strain gauged torque meter attached to the p.t.o. shaft from the gear box measured the torque while an electromagnetic pick-up measured the p.t.o. speed. The draft and lift forces were measured using the technique suggested by Kawamura et al. [11], namely by bonding four strain gages at each of the two lower link pins and the upper link. The draft and lift forces were determined by the bending of the lower link pins and the axial loading of the top link. The inclination of the upper link was measured by a rotary potentiometer attached at the pivot of the tractor lift arm. This potentiometer also measured the depth of subsoiling. The average depth of operation was found to be 462 mm with standard deviation of 2.06 mm. In order to establish local soil resistance, non-oscillating draft was obtained at frequent intervals during the ®eld tests. 2.3. Data analysis The analog data stored on the magnetic tape recorder were converted to digital form through a 16 channel analog to digital converter at the rate of 128 readings per s per channel. A computer program was written to transfer data into the microcomputer for further processing. The average draft and power was determined by integrating the representative portion of the data samples of a test record. A digitizer was used to integrate the time history of the representative samples and a program was also written to determine the area under the curve within the time domain. Statistical analysis of the data was made. The experiment was laid out in a 355 factorial in randomized complete block design with three replications and analyses of variance were made on the draft reduction and power increase. Tables 1 and 2 show the multifactor analysis of variance for the draft ratio and power ratio. These ratios were obtained by dividing the average draft and power requirements for the subsoiler with oscillation by the average draft and power without oscillation at the same forward travel speed. The performance of the subsoiler was expressed in terms of dimensionless draft and power ratios. The operating parameters which were changed were forward speed, amplitude and frequency of oscillation, and the eect of these parameters on the performance was analyzed. A total of 324 tests were conducted, of which 225 were with oscillation and the remainder without oscillation, which served as a control.
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Table 1 Multi-factor analysis of variance for the draft ratio Source of variation
Main eect Speed (S) Frequency (F) Amplitude (A) Interactions SF SA FA Residual Total (corr)
Degrees of freedom
Sum of squares
Mean square
Computed F
10 4 4 2 32 16 8 8 182 224
8.307 0.901 2.052 5.345 0.380 0.108 0.059 0.213 2.907 11.594
0.831 0.455 0.513 1.336 0.012 0.014 0.007 0.013 0.016
52.018** 28.504** 32.119** 83.673** 0.744ns 0.848ns 0.463ns 0.833ns
F-tabulated 5%
1%
1.83 2.37 2.37 2.99 1.42 1.94 1.94 1.64
2.30 3.30 3.30 4.59 1.64 2.49 2.49 2.00
CV=1.49%. *Signi®cant at 5%; **signi®cant at 1%; ns, not signi®cant. Table 2 Multi-factor analysis of variance for power ratio Source of variation
Main eect Speed (S) Frequency (F) Amplitude (A) Interactions SF SA FA Residual Total (corr)
Degrees of freedom
Sum of squares
Mean square
Computed F
10 4 4 2 32 16 8 8 182 224
1.709 0.535 1.003 0.168 0.329 0.180 0.040 0.108 3.219 5.258
0.171 0.268 0.251 0.042 0.010 0.022 0.005 0.067 0.018
9.663** 15.131** 14.216** 2.377ns 0.582ns 1.274ns 0.285ns 0.384ns
F-tabulated 5%
1%
1.83 2.37 2.37 2.99 1.42 1.94 1.94 1.64
2.30 3.30 3.30 4.59 1.64 2.49 2.49 2.00
CV=1.49%. *Signi®cant at 5%; **signi®cant at 1%; ns, not signi®cant.
3. Results and discussion Fig. 2 shows the eect of dierent frequencies, amplitudes and forward speeds on draft ratio. The draft ratio generally decreased with an increase in frequency. This held true for all amplitudes and forward speeds tested. For the same frequency and forward speed, higher amplitude tended to give less draft ratio. The eect of speed on draft ratio varied with amplitude and frequency used. At high amplitudes and frequencies the draft ratio initially decreased slowly with increase in forward speed but increased as the forward speed further increased. Statistical analysis revealed a
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Fig. 2. Eect of frequency, amplitude and forward speed on the draft ratio.
signi®cant eect of forward speed, frequency and amplitude on draft ratio. The reason for observed draft reduction due to oscillation can be explained by the phenomenon that as the frequency and/or amplitude increases the velocity ratio increases, thus reducing the time period during which the share cut the ®rm soil in one cycle. The velocity ratio is de®ned as the peak velocity of tool movement relative to the tractor, divided by forward travel velocity of the tractor. Higher velocity ratios also reduce the frictional resistance on the tool [12]. Even if the velocity ratio is made less than 1, the draft ratio should be reduced since there is a de®nite part of the cycle for which the tool is not cutting the soil. Fig. 3 shows the power ratios as aected by the forward speed, frequency and amplitude. In all experiments conducted it was observed that the average power requirements with oscillation were higher compared to no oscillation. The increased power requirement can be attributed to additional p.t.o. power input for oscillating the machine. In non-oscillating subsoiling, only drawbar power was delivered. Statistical analysis revealed that the frequency, amplitude and forward speed aects the power ratio signi®cantly. At the same frequency and amplitude the power ratio generally decreased as the speed is increased. At an amplitude of 36.5 mm and frequency of 3.7 Hz, the power ratio decreased from 1.12 to 1.05 at 1.85 km hÿ1 and 3.42 km hÿ1 forward speeds, respectively. Increasing the frequency also increased power ratio at the same forward speed and 36.5 mm amplitude of oscillation. In Fig. 2(b), at 2.20 km hÿ1 forward speed and 36.5 mm amplitude, the power ratio increased almost linearly from 1.06 at 3.7 Hz to 1.24 when the frequency was increased to 11.45 Hz. It was revealed that the contribution of p.t.o. power to the total power increased almost linearly with an increase in frequency. The eect of combined interaction of these three parameters on draft and power ratio is generally expressed in terms of the velocity ratio represented by:
E.P. Bandalan et al. / Journal of Terramechanics 36 (1999) 117±125
l
2fa Vo
123
1
where f=oscillating frequency, Hz; a=displacement amplitude, m; and Vo =forward velocity, m/s. The eect of velocity ratio on the draft ratio at dierent amplitudes is shown in Fig. 4. It can be observed that the draft ratio generally decreased with an increase in
Fig. 3. Eect of frequency, amplitude and forward speed on the power ratio.
Fig. 4. Eect of velocity ratio on the draft ratio at dierent amplitudes of oscillation.
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Fig. 5. Eect of velocity ratio on the power ratio at dierent amplitudes of oscillation.
velocity ratio and was less at higher amplitudes. There was a steep reduction in draft ratio up to a velocity ratio of 2.25 beyond which the draft ratio curve showed little decrease with further increase in velocity ratio. From the results it appears that the velocity ratio and amplitude have the strongest in¯uence on the draft reduction. This ®nding con®rmed the results obtained in previous studies, although some scatter was experienced. Fig. 5 presents the eect of velocity ratio on power ratio at dierent amplitudes of oscillation. The power ratio increased slowly with velocity ratio at higher amplitudes and became steep at lower amplitudes of oscillations. By comparing the performance of the subsoiler at dierent operating parameters, it was revealed that an amplitude of 36.5 mm, frequency 9.48 Hz and forward speed 2.20 km hÿ1 gave the lowest draft ratio of 0.33 with a power increase factor of only 1.24 over non-oscillating operation. 4. Conclusions Based on the results of this study, the following conclusions were drawn: (a) The oscillating subsoiler required less draft but higher power than the same sized non-oscillating subsoiler. (b) The draft ratio decreases and the power ratio increases as velocity ratio increases. (c) The implement cannot be operated at frequencies lower than 5 Hz because of the tractor operator discomfort. Sakai et al. [13] reported that the tractor implement system has a fundamental frequency range of 3±5 Hz. It is better to
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operate the subsoiler at frequencies near the fundamental frequency of the soil. (d) It is dicult to obtain the optimum combination of the operating parameters of the subsoiler in actual ®eld situations because it is the velocity ratio which determines optimum performance. In the ®eld the wheel slip cannot be controlled well and each soil condition has dierent fundamental frequency. Acknowledgements The authors are grateful to the Royal Thai Government for ®nancing the project through the National Metal and Material Technology Center, National Science and Technology Development Agency of the Ministry of Science and Technology. The support of the National Agricultural Machinery Center (NAMC), Kasetsart University Research and Development Institute (KURDI) is also acknowledged for the use of its facilities and instruments. References [1] Hammond C, Reid JT, Seigler WE. Seedbed preparation behind row subsoilers. Transactions of the ASAE 1981;24(4):897±901, 904. [2] Niyamapa T. Fundamental studies on soil failure under vibrating tillage machine (part 3). Soil failure under vibrating tillage tool. Journal of Japanese Society Agricultural Machinery 1991;53(5):41±9. [3] Gunn JT, Tramontini VN. Oscillations of tillage implements. Agricultural Engineering 1995;36(11):725±9. [4] Hendrick JG, Buchele WE. Tillage energy of a vibrating tillage tool. Transactions of the ASAE 1963;6(3):213±6. [5] Larson LW. The future of vibratory tillage. Transaction of the ASAE 1967;10(1):78±9, 83. [6] Smith JL, Dais JL, Flikke AM. Theoretical analysis of vibratory tillage. Transactions of the ASAE 1972;15(5):831±3. [7] Johnson CE, Buchele WF. Energy in clod-size reduction of vibratory tillage. Transactions of the ASAE 1967;12(3):371±4. [8] Gupta CP, Rajput DS. Dynamic behavior of the soil under forced vibration. Soil reactions to tillage implements. Final Technical Report of PL480-Scheme. Agricultural Engineering Department, Indian Institute of Technology, Kharagpur, India, 1982. [9] Niyamapa T. Research and Development On Sub-soiler Report (Year I). Kasetsart University, Thailand, 1992. [10] Sakai K, Terao H, Matsui K. The study on vibratory soil cutting by a vibrating subsoiler (Part I). The optimal cutting directional angle. Journal of Japanese Society Agricultural Machinery 1983;45(1):55±62. [11] Kawamura N, Takakita K, Niyamapa T. New concept plow to invert furrow slice at the same position. Research Report on Agricultural Machinery No. 16. Lab of Agricultural Machinery, Kyoto University, Kyoto, Japan. [12] Sharma VK, Drew LO, Nelson GL. High frequency vibrational eects on soil-metal friction. Transactions of the ASAE 1977;20(1):46±51. [13] Sakai K, Hata SI, Takai M, Nambu S. Design parameter of four-shank vibrating subsoiler. Transactions of the ASAE 1993;36(1):330±6.
Performance of an oscillating subsoiler in breaking a hardpan E.P. Bandalan a, V.M. Salokhe a,*, C.P. Gupta a, T. Niyamapa b a Asian Institute of Technology, PO Box 4, Klong Luang, Pathumthani 12120, Thailand Faculty of Engineering, Kasetsart University, Khamphaeng Saen Campus, Nakorn Pathom, Thailand
b
Received 4 May 1998; accepted 9 November 1998
Abstract A single shank tractor mounted oscillating subsoiler was developed to break hardpan, common in sugarcane (Saccharum ocinarum) farms especially after harvest when heavy trucks transport the cut canes from the ®eld to the sugar factory. Field experiments were conducted to determine the optimum combination of performance parameters of the subsoiler. Field tests were conducted at frequencies of oscillation of 3.7, 5.67, 7.85, 9.48 and 11.45 Hz; amplitudes of 18, 21, 23.5, 34 and 36.5 mm; and forward speeds of 1.85, 2.20 and 3.42 km hÿ1 at moisture contents close to the lower plastic limit of the clay soil. A reduction in draft but an increase in total power requirement was found for oscillating compared to nonoscillating subsoiler. The draft and power ratios were signi®cantly aected by the forward speed, frequency and amplitude. Their combined interaction, expressed in terms of the velocity ratio (the ratio of peak tool velocity to forward speed), however, had the strongest in¯uence. At the same velocity ratio, the draft reduction and power increase were less at higher amplitude of oscillation. For the ®eld conditions tested, the optimum operation for least energy expenditure was obtained at an amplitude of 36.5 mm, frequency of 9.48 Hz and speed of 2.20 km hÿ1 with a draft ratio of 0.33 and power ratio of only 1.24. It could be concluded that the oscillating subsoiler reduces draft for breaking hardpan, reduces soil compaction and promotes the use of lighter tractors by utilizing tractor power-take-o (p.t.o.) power to achieve higher eciency of power transmission. # 1999 ISTVS. All rights reserved.
1. Introduction Many soils are susceptible to compaction and the formation of impermeable hardpans below the normal tillage depth. Hammond et al. [1] reported that on * Corresponding author. Tel.:+66-5-524-5450; fax:+66-2-524-6200; e-mail: [email protected] 0022-4898/98/$20.00 # 1999 ISTVS. All rights reserved. PII: S002 2-4898(98)0003 5-4
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E.P. Bandalan et al. / Journal of Terramechanics 36 (1999) 117±125
moist, tilled sandy soil, 2 to 5 cm-thick pans are formed quite easily after a few trips by tillage machines. Hardpans inhibit root penetration and cause drainage problems which result in reduced crop yields. In Thailand, hardpan formations are common in sugarcane ®elds, especially after harvesting when heavy trucks transport the cut cane from the ®eld to the sugar factory. The ®elds are subsoiled annually to break through and shatter these soil layers to improve drainage for the next crop [2]. The utilization of the tractor p.t.o. power for tillage is not common among Thai farmers and subsoiling is done conventionally, thus requiring very high draft and hence tractor ballasting which consequently results in additional compaction. The vibration of soil engaging tools, like blades, tines or shares has been known to reduce the draft force needed to pull the implement. This is highly desirable for high draft implements such as subsoilers. Such draft reduction has been studied and veri®ed by many researchers including Gunn and Tramontini [3], Hendrick and Buchele [4], Larson [5], and Smith et al. [6]. The use of vibration in tillage also produces better soil breakup, although the total power requirement may not be reduced [6,7]. However, for a certain degree of pulverization, the total energy input per unit mass will be smaller compared to non-vibratory tillage since secondary tillage is minimized [5]. With the reduction in draft for soil cutting using vibratory tillage, it is therefore possible to accomplish high draft requirement operations such as subsoiling with relatively lighter tractors and thus soil compaction can be reduced. Gupta and Rajput [8] studied the eect of amplitude and frequency on soil breakup by an oscillating tillage tool in a soil bin experiment. It was observed that the maximum utilization of energy occurs at an oscillation frequency close to natural frequency of soil. At any frequency, soil break-up increased with increase in amplitude. Niyamapa [9] developed a full scale single oscillating subsoiler intended for the use in sugarcane farms in Thailand. Preliminary investigations showed that it may well be adaptable locally under certain operating conditions. This subsoiler utilizes the tractor p.t.o. power which has higher eciency of power transmission as compared to a passive type subsoiler which utilizes drawbar power. The objective of this study was to test the performance of this oscillating subsoiler under actual ®eld conditions and to establish its optimum operating parameters. Speci®cally, the study was conducted to determine the draft and total power required for soil break-up by the vibratory subsoiler at selected amplitudes, frequencies of oscillation, and forward speeds; and determine the combination of amplitude of oscillation, vibration frequency and forward speed for optimum draft and total power requirement. 2. Materials and methods 2.1. Description of the test site The experiments were conducted at the Kasetsart University, Khampaeng Saen Campus, Nakorn Pathom, Thailand. A one hectare sugarcane ®eld (clay soil) which had already been used as aprons for cane carrying trucks was used for ®eld testing.
E.P. Bandalan et al. / Journal of Terramechanics 36 (1999) 117±125
119
It contained clay with a liquid limit of 28%, plastic limit 22%, cohesion 19.15 kPa, adhesion 4.0 kPa and angle of internal friction 31.4 . The average cone index of the ®eld was 1414 kPa over a depth of 60 cm but the soil strength varied within the area. Hence the area was divided into three blocks having cone indices ranging from 1352 to 1984 kPa (average 1669 kPa) for the ®rst block; 996 to 1765 kPa (average 1422 kPa) for the second and 799 to 1675 kPa (average 1150 kPa) for the third block. Soil bulk density was determined at every 150 mm to 600 mm depth. The average densities were 14.6, 15.5, 15.2, 15.3 kN/m3 at depths 0±150 mm, 150±300 mm, 300± 450 mm and 450±600 mm, respectively. Moisture content of the surface soil (0± 150 mm) varied during the test from 8 to 21.2% and that of second layer (150± 300 mm) from 9 to 27%. However, the moisture condition near the average operating depth of 462 mm was relatively constant, varying from 18 to 22%. 2.2. Test machine and instrumentation A schematic of the oscillating subsoiler is shown in Fig. 1. The tine attached at the bottom of the standard was 400 mm long having a cutting edge of 70 mm width and a lift angle of 30 as recommended by Sakai et al. [10]. Oscillation was accomplished through an eccentric shaft connected to the upper end of the share so that it can be moved forward and backward. The amplitude was varied between 18, 21, 23.5, 34 and 36.5 mm by using crank shafts of dierent eccentricities. Power was transmitted to the crank shaft from the tractor p.t.o. through a pair of spiral-bevel gears having
Fig. 1. Schematic diagram of oscillating subsoiler [9].
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E.P. Bandalan et al. / Journal of Terramechanics 36 (1999) 117±125
a speed reduction of 3.75 and then to a sprocket and chain with a ratio which can be varied depending on the desired frequency and the p.t.o. speed. To minimize forward speed variation, the engine speed was set to give 540 p.t.o. rpm during the test and the frequency was varied by changing sprocket combinations. The desired frequencies of 3.7, 5.67, 7.58, 9.48 and 11.45 Hz were obtained by using the sprocket reductions of 2.25, 1.5, 1.125, 0.9 and 0.75, respectively. Average forward speeds of 1.84, 2.20 and 3.42 km hÿ1 were obtained by selecting dierent gear ratios. The tractor used was a 43-kW KUBOTA model 5500 DT. The instrumentation system included the measurement of forces in the connecting links, torque, rpm, operating depth and angle of inclination of the upper link. For the strain gauge transducers, a six-channel auto-balancing strain ampli®er was used to amplify the signals. All measurements were recorded on a seven channel magnetic tape recorder for further analysis. A strain gauged torque meter attached to the p.t.o. shaft from the gear box measured the torque while an electromagnetic pick-up measured the p.t.o. speed. The draft and lift forces were measured using the technique suggested by Kawamura et al. [11], namely by bonding four strain gages at each of the two lower link pins and the upper link. The draft and lift forces were determined by the bending of the lower link pins and the axial loading of the top link. The inclination of the upper link was measured by a rotary potentiometer attached at the pivot of the tractor lift arm. This potentiometer also measured the depth of subsoiling. The average depth of operation was found to be 462 mm with standard deviation of 2.06 mm. In order to establish local soil resistance, non-oscillating draft was obtained at frequent intervals during the ®eld tests. 2.3. Data analysis The analog data stored on the magnetic tape recorder were converted to digital form through a 16 channel analog to digital converter at the rate of 128 readings per s per channel. A computer program was written to transfer data into the microcomputer for further processing. The average draft and power was determined by integrating the representative portion of the data samples of a test record. A digitizer was used to integrate the time history of the representative samples and a program was also written to determine the area under the curve within the time domain. Statistical analysis of the data was made. The experiment was laid out in a 355 factorial in randomized complete block design with three replications and analyses of variance were made on the draft reduction and power increase. Tables 1 and 2 show the multifactor analysis of variance for the draft ratio and power ratio. These ratios were obtained by dividing the average draft and power requirements for the subsoiler with oscillation by the average draft and power without oscillation at the same forward travel speed. The performance of the subsoiler was expressed in terms of dimensionless draft and power ratios. The operating parameters which were changed were forward speed, amplitude and frequency of oscillation, and the eect of these parameters on the performance was analyzed. A total of 324 tests were conducted, of which 225 were with oscillation and the remainder without oscillation, which served as a control.
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121
Table 1 Multi-factor analysis of variance for the draft ratio Source of variation
Main eect Speed (S) Frequency (F) Amplitude (A) Interactions SF SA FA Residual Total (corr)
Degrees of freedom
Sum of squares
Mean square
Computed F
10 4 4 2 32 16 8 8 182 224
8.307 0.901 2.052 5.345 0.380 0.108 0.059 0.213 2.907 11.594
0.831 0.455 0.513 1.336 0.012 0.014 0.007 0.013 0.016
52.018** 28.504** 32.119** 83.673** 0.744ns 0.848ns 0.463ns 0.833ns
F-tabulated 5%
1%
1.83 2.37 2.37 2.99 1.42 1.94 1.94 1.64
2.30 3.30 3.30 4.59 1.64 2.49 2.49 2.00
CV=1.49%. *Signi®cant at 5%; **signi®cant at 1%; ns, not signi®cant. Table 2 Multi-factor analysis of variance for power ratio Source of variation
Main eect Speed (S) Frequency (F) Amplitude (A) Interactions SF SA FA Residual Total (corr)
Degrees of freedom
Sum of squares
Mean square
Computed F
10 4 4 2 32 16 8 8 182 224
1.709 0.535 1.003 0.168 0.329 0.180 0.040 0.108 3.219 5.258
0.171 0.268 0.251 0.042 0.010 0.022 0.005 0.067 0.018
9.663** 15.131** 14.216** 2.377ns 0.582ns 1.274ns 0.285ns 0.384ns
F-tabulated 5%
1%
1.83 2.37 2.37 2.99 1.42 1.94 1.94 1.64
2.30 3.30 3.30 4.59 1.64 2.49 2.49 2.00
CV=1.49%. *Signi®cant at 5%; **signi®cant at 1%; ns, not signi®cant.
3. Results and discussion Fig. 2 shows the eect of dierent frequencies, amplitudes and forward speeds on draft ratio. The draft ratio generally decreased with an increase in frequency. This held true for all amplitudes and forward speeds tested. For the same frequency and forward speed, higher amplitude tended to give less draft ratio. The eect of speed on draft ratio varied with amplitude and frequency used. At high amplitudes and frequencies the draft ratio initially decreased slowly with increase in forward speed but increased as the forward speed further increased. Statistical analysis revealed a
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Fig. 2. Eect of frequency, amplitude and forward speed on the draft ratio.
signi®cant eect of forward speed, frequency and amplitude on draft ratio. The reason for observed draft reduction due to oscillation can be explained by the phenomenon that as the frequency and/or amplitude increases the velocity ratio increases, thus reducing the time period during which the share cut the ®rm soil in one cycle. The velocity ratio is de®ned as the peak velocity of tool movement relative to the tractor, divided by forward travel velocity of the tractor. Higher velocity ratios also reduce the frictional resistance on the tool [12]. Even if the velocity ratio is made less than 1, the draft ratio should be reduced since there is a de®nite part of the cycle for which the tool is not cutting the soil. Fig. 3 shows the power ratios as aected by the forward speed, frequency and amplitude. In all experiments conducted it was observed that the average power requirements with oscillation were higher compared to no oscillation. The increased power requirement can be attributed to additional p.t.o. power input for oscillating the machine. In non-oscillating subsoiling, only drawbar power was delivered. Statistical analysis revealed that the frequency, amplitude and forward speed aects the power ratio signi®cantly. At the same frequency and amplitude the power ratio generally decreased as the speed is increased. At an amplitude of 36.5 mm and frequency of 3.7 Hz, the power ratio decreased from 1.12 to 1.05 at 1.85 km hÿ1 and 3.42 km hÿ1 forward speeds, respectively. Increasing the frequency also increased power ratio at the same forward speed and 36.5 mm amplitude of oscillation. In Fig. 2(b), at 2.20 km hÿ1 forward speed and 36.5 mm amplitude, the power ratio increased almost linearly from 1.06 at 3.7 Hz to 1.24 when the frequency was increased to 11.45 Hz. It was revealed that the contribution of p.t.o. power to the total power increased almost linearly with an increase in frequency. The eect of combined interaction of these three parameters on draft and power ratio is generally expressed in terms of the velocity ratio represented by:
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l
2fa Vo
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1
where f=oscillating frequency, Hz; a=displacement amplitude, m; and Vo =forward velocity, m/s. The eect of velocity ratio on the draft ratio at dierent amplitudes is shown in Fig. 4. It can be observed that the draft ratio generally decreased with an increase in
Fig. 3. Eect of frequency, amplitude and forward speed on the power ratio.
Fig. 4. Eect of velocity ratio on the draft ratio at dierent amplitudes of oscillation.
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Fig. 5. Eect of velocity ratio on the power ratio at dierent amplitudes of oscillation.
velocity ratio and was less at higher amplitudes. There was a steep reduction in draft ratio up to a velocity ratio of 2.25 beyond which the draft ratio curve showed little decrease with further increase in velocity ratio. From the results it appears that the velocity ratio and amplitude have the strongest in¯uence on the draft reduction. This ®nding con®rmed the results obtained in previous studies, although some scatter was experienced. Fig. 5 presents the eect of velocity ratio on power ratio at dierent amplitudes of oscillation. The power ratio increased slowly with velocity ratio at higher amplitudes and became steep at lower amplitudes of oscillations. By comparing the performance of the subsoiler at dierent operating parameters, it was revealed that an amplitude of 36.5 mm, frequency 9.48 Hz and forward speed 2.20 km hÿ1 gave the lowest draft ratio of 0.33 with a power increase factor of only 1.24 over non-oscillating operation. 4. Conclusions Based on the results of this study, the following conclusions were drawn: (a) The oscillating subsoiler required less draft but higher power than the same sized non-oscillating subsoiler. (b) The draft ratio decreases and the power ratio increases as velocity ratio increases. (c) The implement cannot be operated at frequencies lower than 5 Hz because of the tractor operator discomfort. Sakai et al. [13] reported that the tractor implement system has a fundamental frequency range of 3±5 Hz. It is better to
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operate the subsoiler at frequencies near the fundamental frequency of the soil. (d) It is dicult to obtain the optimum combination of the operating parameters of the subsoiler in actual ®eld situations because it is the velocity ratio which determines optimum performance. In the ®eld the wheel slip cannot be controlled well and each soil condition has dierent fundamental frequency. Acknowledgements The authors are grateful to the Royal Thai Government for ®nancing the project through the National Metal and Material Technology Center, National Science and Technology Development Agency of the Ministry of Science and Technology. The support of the National Agricultural Machinery Center (NAMC), Kasetsart University Research and Development Institute (KURDI) is also acknowledged for the use of its facilities and instruments. References [1] Hammond C, Reid JT, Seigler WE. Seedbed preparation behind row subsoilers. Transactions of the ASAE 1981;24(4):897±901, 904. [2] Niyamapa T. Fundamental studies on soil failure under vibrating tillage machine (part 3). Soil failure under vibrating tillage tool. Journal of Japanese Society Agricultural Machinery 1991;53(5):41±9. [3] Gunn JT, Tramontini VN. Oscillations of tillage implements. Agricultural Engineering 1995;36(11):725±9. [4] Hendrick JG, Buchele WE. Tillage energy of a vibrating tillage tool. Transactions of the ASAE 1963;6(3):213±6. [5] Larson LW. The future of vibratory tillage. Transaction of the ASAE 1967;10(1):78±9, 83. [6] Smith JL, Dais JL, Flikke AM. Theoretical analysis of vibratory tillage. Transactions of the ASAE 1972;15(5):831±3. [7] Johnson CE, Buchele WF. Energy in clod-size reduction of vibratory tillage. Transactions of the ASAE 1967;12(3):371±4. [8] Gupta CP, Rajput DS. Dynamic behavior of the soil under forced vibration. Soil reactions to tillage implements. Final Technical Report of PL480-Scheme. Agricultural Engineering Department, Indian Institute of Technology, Kharagpur, India, 1982. [9] Niyamapa T. Research and Development On Sub-soiler Report (Year I). Kasetsart University, Thailand, 1992. [10] Sakai K, Terao H, Matsui K. The study on vibratory soil cutting by a vibrating subsoiler (Part I). The optimal cutting directional angle. Journal of Japanese Society Agricultural Machinery 1983;45(1):55±62. [11] Kawamura N, Takakita K, Niyamapa T. New concept plow to invert furrow slice at the same position. Research Report on Agricultural Machinery No. 16. Lab of Agricultural Machinery, Kyoto University, Kyoto, Japan. [12] Sharma VK, Drew LO, Nelson GL. High frequency vibrational eects on soil-metal friction. Transactions of the ASAE 1977;20(1):46±51. [13] Sakai K, Hata SI, Takai M, Nambu S. Design parameter of four-shank vibrating subsoiler. Transactions of the ASAE 1993;36(1):330±6.