Florin Paper 5-05-2009 Articol Buletin 2009 Final Florin

Bulletin of the Transilvania University of Braşov • Vol. 2 (51) - 2009 Series II: Forestry • Wood Engineering • Agriculture and Food Engineering

THEORETICAL CONTRIBUTIONS TO THE CINEMATIC OPTIMIZATION OF INTERMITTENT MECHANICAL TRANSMISSIONS WHICH EQUIP THE SEED DRILLS Florin LOGHIN1 Abstract: In this paper is presented the method of simulation computer-assisted of the kinematics of the mechanism cam-balance lever used in the transmissions of the seed drill for cereals, through the application of Animation-Mechanism approach of the software ProEngineer Wildfire 2.0. The results of research through simulation are presented in the likeness of diagrams which emphasize the functional peculiarities of the mechanism cambalance lever.

Key words: seed drill, transmissions, simulation. 1. Introduction In order to assured the correlation among the speed of movement machine and the amount of seeds N which is delivered on surface unit, the dosage machines and the agitator systems of seeds from the seeds box of seed drill strawy cereals, receive rotation motion from the active wheel through transmissions with intermittent function which have in their component variator with mechanims cam-balance wheel and one-way coupling, which from theoretical point of view, permit realization of increased number of conduction reports, with more reduced number of constitutive elements submissive to detrition (Figure 1) [1], [ 4]. The variator with intermittent operation is composed by a number conditioned of mechanisms cam-balance wheel, mounted inline, these operating phase-shifted, therethrough following the enlargement of uniformity motion of rotation of secondary arbor ( Figure 2). The variator with cam-balance wheel transforms the contiguous motion, with constant angular speed, of input arbor, on the move 1

variable intermittent the arbor of exit. To the base of variator operation, with intermittent motion, stands the principle of summarization impulses of rotation, generate of the ensemble cam - balance wheel – one-way coupling. The motion of variable rotation of exit arbor is made through the modification of active race ∆Ψ of the balance wheel (Figure 2), through limitation of this return, by dint of plate of limitation [2]. During a completely rotations of cam, the balance wheel is acted of these lobes, for each lobes of the cam, executing a motion of oscillation which represents the active race, with an angle which value is determinated of minimum and maximum radius of cam profile. The race of return of each balance wheel is a passive race, and is achieved below of drive of helical bows, pre-tensionated, this beeing limited of limiter plate, through their position checking up the value of angle of gear the reel with the cam. Limiter plate is fixed on an arbor, foreseed with a mechanic system of index, the posture limiter plate beeing adequate on a sector calibrated [3]. From functional viewpoint, the balance wheel

Dept. of Food Products Engineering, Transilvania University of Braşov.

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Bulletin of the Transilvania University of Braşov • Vol. 2 (51) - 2009 • Series II

which is mounted on exterior ring of one-way coupling, executes the role of an oscillatory cam follower with reel. The one-way coupling

transmits the torque and the motion of rotation between the exterior and the internal ring, just for active race of the balance wheel.

Fig. 1. Variator with mechanisms cam – balance lever: 1 - reductor; 2 - cams; 3 - oscilatory cam follower; 4 - reels; 5 – one-way couplings; 6 - helical bows; 7 – stop plate; 8 – lever for stop plate position; 9 – calibrated sector; 10 – intermediate arbor; 11 exit arbor; 12 - system of assembling of variator on machine. 2. Material and Method The computer-assisted simulation of the mechanisms cam-balance lever operation. As part as simulation, the race of return of the balance wheel was determined for different values of angle position of plate of limit this race (Figure 2, a). For the determination of extreme positions of limiter plate of race were considered the positions of the cam, respectively of balance wheel, which characterizes the minimum respective maximum race of the balance wheel (Figure 2, b). For the simulation of mechanism kinematic was used the module Animation-Mechanism of ProEngineer Wildfire 2.0 software. The module Animation-Mechanism is used for visualization of a mechanism motion or of a functional mechanic ensemble [5]. In order for Animation-Mechanism module can operate in optimum conditions, was applied a

simplified model of a variator with intermittent motion, neglecting the two one-way couplings of one-way traffics, wherethrough the balance wheels are kinematic binded of exit arbor. This simplification is motivated through the next: - the simulation is attained just for the analysis of rotation angle of the cams and the race of balance wheels; In first stage of simulation mechanism operation, was accomplished the representation of all pieces and modules which compose the mechanism, whereafter were put the restrictions advert to assemblage manner, wherethrough was attain corrected poition of all the component elements of the ensemble. For the representation of component elements of the gearbox were utilized the drawings of execution of these. For the application of assemblage restrictions was necessary the cognition of the next questions: position of the piece in report with the bindery pieces and the category of specific restriction, for

Fl. Florin.: Theoretical contributions to the cinematic optimization of intermittent mechanical transmissions which equip the seed drills

several of them. To assure the correct operation of the mechanism, for the fixed pieces, which don't assist to conduction motion, were put Place

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type restrictions and for the mobile pieces, between is transmited the motion, were put Connect type restrictions.

a. b. Fig. 2. The schernatic scheme of cam - balance wheel mechanism, utilized in the simulation.

a. b. Fig. 3. The scheme of the cam gear : a. with five lobes; b. with four lobes: 1 – balance wheel; 2 - stop plate; 3 - the arbor of stop plate; 4 – helical bows; 5 – cam; 6 – input arbor; 7 – the reel of balance wheel; 8 – exit arbor.

- the couplings contain a big number of elements, which requires, on their ensemble, a very big number of restrictions, which ProEngineer software cannot to generate them. The second stage in simulation realization was adverted to application of restrictions of kinematic order, which are compulsions which generates the motion of leading elements of

mechanism, depending on time, and the application of input motion to the leading element. First restriction of kinematic order is related to the fact that during of active race the reels 6 of the balance wheels 1 (Figure 3, a) is displaced on the cam profile and have the possibility of detachments from this, at the end of passive race. For this compulsion is utilized command Cam -

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Bulletin of the Transilvania University of Braşov • Vol. 2 (51) - 2009 • Series II

Follower Connections, with the property Enable Liftoff. The second restriction of kinematic order is related to the possibility limitation of the race of the return of balance wheels, therefor beeing used the command Cam - Follower Connections, with the propriety Enable Liftoff, and property Enable Friction. The third restriction of kinematic order is related to the fact that on an area of return race, up to the contact with the limiter plate, is necessary the sustentation of balance wheels reels in contacts with the cam profile, therefor using the command Springs, wherethrough is generated helical bows mounted in pre-tension state. To adopt the value of tensions from the helical bows, exists the possibility of modification values of elastic constant K or diameter of wrap up the whorls. For generation the motion of camshaft was used Motors command, the software permiting modification of the rev. After runing through these stages, was obtained the mechanisms presented in the figure 3. As part as this works was took under consideration the possibility of kinematic simulation of two types of mechanisms cam balance wheel: with two cams with five lobes, mounted in-line, the lobes beeing phase-shifted with 36 of degrees (Figure 3, a) and respective with three cams, with four lobes, mounted inline, the lobes beeing phase-shifted with 30 degrees (Figure 3, b).

Fig. 4. The diagram of variation of oscillation angle of cam follower depending on time, for the case of maximum race.

Fig. 5. The diagram of variation of oscillation angle of cam follower depending on time, for the case of minimum race.

3. Results and Discussions Abaft simulation, the result of theoretical research were visualized through charts, in which was represented the variation of the balance wheel race depending on time, and enable an easy analysis connected with the balance wheels motion, for different positions of plate of limit return race ( Figures 4, 5, 6).

Fig. 6. The diagram of variation of oscillation angle of cam follower depending on time, for the case of intermediate race.

Fl. Florin.: Theoretical contributions to the cinematic optimization of intermittent mechanical transmissions which equip the seed drills

The theoretical research through simulation was achieved in the next conditions: the rev of input arbor 0,33 rot/s, the cam with four lobes type, and for the plate limiter were adopted three significant positions: the proper position of maximum race of cam follower, when the reel of balance wheel doesn't detached from the cam profile (Figure 4); the proper position of minimum race cam follower, when the reel of the balance wheel touches the flank of the lobe just in the zone of this peak (Figure 5) and an intermediate position wherewith is assured the gearing of the reel of the cam follower on a half from his race (Figure 6).

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In the charts presented, the point A characterized the moment of finish the active race and the begining of the race retractive, the reel cam follower beeing on the peak of the lobe of the cam; The point B characterizes the moment in which the cam follower gets in touch with the plate limiter, what facts represent the end of passive race; the point C characterizes the moment in which the cam follower gets in touch with the profile of the lobe of the cam and begins the active race; the point D characterizes the finish of the active race.

Fig. 7. The diagram of variation of oscillation angle and velocity of cam follower depending on time. The report of conduction between input arbor and the one of exit is defined as the report among the angles of turnings of input arbor and the arbor of exit, on duration of an operation cycle.For the case in which the cam follower executes the angular minimum race (Figure 5), sector BC with

duration of 1,4 second, characterizes the period in which the cam follower is rested on limiter plate, the angle of oscillation of the balance wheel beeing approximatively 1,2 degrees. The report of conduction between the input arbor and one of exit is 37,5.

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Bulletin of the Transilvania University of Braşov • Vol. 2 (51) - 2009 • Series II

For intermediate values of the race of the cam follower (Figure 6), sector BC is decreased, the report of conduction between the input arbor and one of exit taking the values in determinated interval. In the Figure 7 is presented the diagram of variation of oscillation angle and of angular speed of the balance wheels, for the mechanism with two cams with five lobes (for maxim race). The variation law of angular space goed through by drill arbor of dosage machines is in the likeness of a succession of impulses and is explained through the fact that to the base of these gearboxes operation stands the principle of summarization of the impulses obtained from cam-balance lever mechanisms. In the Figure 8 is presented the temporally variation of angular space goed through by drill arbor of the dosage machines (exit arbor) for the case in which this receives the motion of rotation by dint of the mechanism with two cams with five lobes. In order to noticed better the unlevelness of arbor motion was selected a report of big conduction of gearbox with operation in impulses, respectively a minor rev of drill arbor of the dosage machines.

Fig. 8. The diagram of variation of spin angle of exit arbor depending on time. 4. Conclusions To the base of operation of this variator type stands the principle of summarization of impulses generated by several cams lobes and the transformation of motion oscillation of the

balance wheels on the move of intermittent rotation of exit arbor of variator by dint of oneway coupling. The computer-assisted simulation of operation of cam - balance wheel – one way coupling box consisted in the representation in 3D of mechanisms and the graphic representation of angular space variation, described by points of balance wheels. The charts were put in evidence the fact that the form of impulses is stricken direct of: the number of cams of gearbox, the number of lobes of these and of position limiter plate of race to revert of balance wheel. The method permited easy determination of minimum and maximum report of variation, what is attain of the variator. References

1.Loghin, Fl., Hodîrnău, M, The cinematic analyze computer - assisted of the gearbox with intermittent function used to the seed drill, Proceeding of BIOATLAS, vol. 2., 2008. 2.Loghin, Fl., Cutie de viteze cu impulsuri pentru reglarea debitului de seminţe la apratele de distribuţie ale semănătorii de cereale (Gearbox with impulses for adjustment of the flow of seeds to distribution machines of seed drills), The mechanization of agriculture, No. 1-2, 2007. 3.Marin, E., Mecanisme cu came pentru transmisia distribuţiei maşinilor de semănat cereale păioase (Cam gears for transmission of distribution of the seed drills strawy cereals), Ed. The terra Nostra, Iaşi, 2007. 4.Rus, Fl., Masini agricole pentru lucrarile solului, semanat si intretinerea culturilor (Agricultural machines for the works of soil, sowing and maintenance the cultures)," Transilvania" University from Brasov, 1987. 5.*** Creating Flexible Components in Pro/ENGINEER Wildfire - a tutorial to create part flexibility and assembly variation, 2006.