Science in China Series E: Technological Sciences? 2007 Science in China PressSpringer-VerlagStudy of utilizing differential gear train toachieve hybrid mechanism of mechanicalpressHE YuPeng1?, ZHAO ShengDun2, ZOU Jun2 2 School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, ChinaThe problems of hybrid input of mechanical press are studied in this paper, withdifferential gear train as transmission mechanism. It is proposed that “adjustable-speed amplitude” or “differential-speed ratio” is the important parameters forthe hybrid input mechanism. It not only defines the amplitude of the adjustablespeed, but also determines the ratio of the power of the servomotor to the power ofthe conventional motor. The calculating equations of the ratio of transmission in allaxes, the power of two motors, and the working load distribution are deduced. Thetwo kinds of driving schemes are put forward that the servomotor and the conventionalmotor simultaneously drive and the servomotor and the conventional motorseparately drive. The calculating results demonstrate that the latter scheme canuse much lower power of the servomotor, so this scheme makes manufacture anduse cost much lower. The latter scheme proposes a feasible way to apply the hybridmechanism of mechanical press in practice engineering.mechanical press, hybrid mechanism, differential gear train, adjustable-speed1 IntroductionAt present there are many research papers about the hybrid mechanism of mechanical press, and ithas become a hot research topic. The hybrid mechanism is a mechanism with 2-degree-of freedom(also called differential speed mechanism), and when two independent motions are input at thesame time, the output that can satisfy some motion requirements is obtained through the motioncomposition of the mechanism. The hybrid mechanism is also called controllable mechanism, orhybrid machine. The purpose of research on hybrid mechanism of mechanical press is using conventional motor with big power carrying flywheel to finish stamping work pieces; and uses ser —vomotor with low power to adjust the slider speed. The advantages of the hybrid mechanism applied in the mechanical press are that it not only can reduce much lower manufacturing cost than servo press, but also has a flexible working velocity of slider[1]. So the mechanical press of hybrid mechanism arouses many researchers’ interest in working on it; and these studies are mainly focused on the multi-bar hybrid mechanism. Du and Guo[1, 2] have comprehensively discussed the seven-bar hybrid mechanism of mechanical press, including the feasible conditions of composition of the linkage mechanism, the slider motion analysis, and the torque and power distribution between the two motors as well as the optimal design. The trajectory planning based on polynomial interpolation is also investigated, and the computer simulation shows that the result is indeed attractive. In addition, Meng[3] has also investigated the kinematical analysis of the seven-bar mechanism, and the optimal design has been completed based on the minimum power of the servomotor motor, and Meng has proposed that the hybrid mechanism is a research direction of the mechanical press. Tokuz[4] first put forward of the hybrid mechanism and analyzed the velocity synthesis by using the differential gear train. His experiment confirmed the feasibility of his conception. The concepts of the adjustable-speed amplitude and differential-speed ratio are not mentioned in their works, and the relationship between the velocity variation and the power of the two motors were not clearly given[5―8]. But these concepts are very important and absolutely necessary for the hybrid mechanism to select the two motors’ power and determine the working load distribution between conventional motor and the servomotor. In refs. [1―3] they used linkage mechanism to implement the hybrid input of mechanical press. The method is very complex because the change of the length and position of the each bar in linkage mechanism will have an effect on the motion of the slide of the mechanical press. So some principal problems are usually ignored in research hybrid mechanism course, and the research results don not always coincide with the practice engineering conditions[9―11]. The gear differential train has two freedoms, and the ratios of transmission between arbitrary two axes are a constant. In order to simplify the mechanical model and make the problems much projected, the differential gear train is used as transmission mechanism to study the hybrid problems of the mechanical press in this paper. This paper addresses the relationship between the adjustable-speed amplitude and the power of the two motors, the working load distribution between the two motors, and puts forward two drive schemes of the conventional motor and the servomotor simultaneously working, and two motors separately working. With the 200-ton mechanical press as the engineering background, a drive system of the hybrid mechanism of the mechanical press is designed, and the feasibility of the two drive schemes in mechanical press is analyzed.2 The principle of the hybrid mechanismThe working principle of the hybrid mechanism of the mechanical press with differential gear train is illustrated in Figure 1. The system consists of conventional motor (also called AC machine with constant speed), servomotor, reducing unit I, reducing unit II, differential gear train, and crank slide mechanism. The output axis of the differential gear train is connected with the crankshaft of the crank slide mechanism. One of the two input axes links the conventional motor through the reducing unit ?; the other input axis links the servomotor through the reducing unit II. Therefore the motion of the crankshaft is completely controlled by the motions of the conventional motor and the servomotor. The reducing unit ? and the reducing unit II are respectively installed between the two motors and the differential gear unit in the way of serial in order to bear a part of reducing velocity task of the all transmission system, because too big drive ratio of the differential gear train will make its driving efficiency decreased. The angular velocity of the conventional motor is constant, so its price is cheaper. The angular velocity of the servomotor is adjustable, so its price is expensive. In the system of the hybrid mechanism the constant speed of the output axis is provided by high power conventional motor; and the servomotor provides its adjustable speed. Therefore, in this way, it not only makes the output motion of the crankshaft of the mechanical press flexible, but also avoids using high power servomotor. Hence it could save both the machine manufacturing costs and the machine operating costs.Figure 1 Working principle of hybrid mechanism of differential gear train.3 The velocity characteristics of the mechanical press slideThe work of the mechanical press presents the regularity of the periodic change[12]. The displacement and velocity changes of the mechanical press slide in an ideal work circulation areillustrated in the Figure 2. The slide starts to move from top dead center to the working start point at high velocity (called quick feeding stage). When the slide of mechanical press approaches theworking point, its high velocity is shifted to slow velocity and then it begins to stamp work piece at low velocity (called low working stage). The low velocity of the slide is to avoid great impact on the die, and benefit the plastic shaping of the work piece. After the slide finishes the stamping work and reaches the bottom dead center, the slide comes back at high velocity and stops at the top dead center (called quick back stage). Hence, the motion velocity of the mechanical press slide can be divided three kinds: high down velocity V1 , slow working velocity V2 , and high back velocity V3 . The velocity V1 and velocity V3 should be as possible as high and the velocity V2 should be slow and flexible in order to ensure high working times of the mechanical press per minute and satisfy the requirements of different technologies. Actually the mechanical press only works in a very short course before the bottom dead center, and in the other courses it does not do work to the work piece.4 The nomenclatures and equations of the hybrid mechanism4.1 The relationship of the angular velocity in all axesThere are three external axes in the differential gear train as illustrated in Figure 1. In order toconveniently express the relationship of the three axes, the axis connected with the conventionalmotor is called axis 1, the axis connected with servomotor is called axis 2, and the axis connectedwith crankshaft is called axis 0. The angular velocities of the three axes are respectively expressedas n1 , n2 and n0 . The torques of the three axes are respectively expressed as M1 , M2 and M0 .Because there are two freedoms in the differential gear train, only the third axis is fixed, such thatthe drive ratio of the other two axes can be determined. So the relationships of drive ratio andangular velocity of the three axes need to be expressed as the character with superscript and subscript.Figure 2 Ideal displacement cure of the slide.4.1.1 The conventional motor’s influence on the output motion. When the servomotor stops, n2 = 0 , only the angular velocity of the conventional motor affects the output angular velocity n0 .4.1.2 The servomotor’s influence on the output motion. When the conventional motor stops, n1 = 0 , only the angular velocity of the servomotor affects the output angular velocity n0 , where 1 n0 represents axis 0 angular velocity, and 1 i20 represents total drive ratio from axis 2 to axis 0 including differential gear train and reducing unit II when axis 1 (servomotor axis) is fixed.4.1.3 The conventional motor’s and servomotor’s influence on the output motion. When the conventional motor and the servomotor run at the same time through the composition of the differential gear train, the output velocity can be expressed as . Because the servomotor can run at arbitrary angular velocity between the zero and specific velocity in both positive and negative directions, n2 can be expressed as .where K is the ratio of the actual angular velocity to the specific angular velocity of the servomotor; the value is arbitrary between ?1 and +1, including zero. n2e is the specific angular velocity of the servomotor. 4.2 Adjustable-speed amplitude and differential-speed ratio4.2.1 Adjustable-speed amplitude. In order to correctly denote the variable velocity of the differential gear train of the hybrid mechanism, the concept of adjustable-speed amplitude is introduced. As shown in Figure 1, adjustable-speed amplitude is the ratio (or percentage) of absolute value of up and down adjustable amount to the base speed. In the differential gear train of the hybrid mechanism, the adjustable-speed amplitude equals the ratio value of axis 0 output speed of operating a single servomotor at the specific speed to axis 0 output speed of operating a single conventional motor[13]. In the differential gear train of the hybrid mechanism, the adjustable-speed amplitude is the most basic and the most important technology parameter. It not only determines the matching relationship of the speed of the two input axes, but also decides the matching relationship of the installed capacity of the servomotor and the conventional motor4.2.2 Differential-speed ratio.The differential-speed ratio is usually used to express adjustable speed technology performance in the differential gear train. It is an important technology parameter of the differential effect in the differential system. The differential-speed ratio equals the reciprocal value of the adjustable-speed amplitude. It can be expressed as According to the fact that the angular velocity is in inverse proportion to its torque and that the same load is driven by conventional motor and servomotor, an equation expressed with the powers of the two motors can be deduced, where P1 is the power of the conventional motor, P1 = M1n1 . P2 is the power of the servomotor, P2 = M2n2e .4.3 The working load power distributionSupposing that the working load power of the mechanical press is P0 , the power relationshipbetween the conventional motor, the servomotor and working load can be expressed as below:Figure 3 Physical sense of the adjustable-speed amplitude.From eqs. (9)―(11), the output powers of the conventional motor and the servomotor are determined by the value of factor K, which is actually equal to the change ratio of angular velocity of the servomotor. Hence when the output angular velocity runs in different working region, the ratio of bearing load of the two motors is different, too.4.3.1 The output axis running at the basic speed.When the output angular velocity of the servomotor equals zero, that is, K = 0 , P2 = 0 , fromeq. (9), we have .Here the conventional motor bears all the loading power.4.3.2 The output axis running in the increasing speed region.The servomotor runs in the positive direction, 0≤K≤1 , and both P1 and P2 are positive values, so both the conventional motor and the servomotor bear a part of the working load. Thus the conventional motor bears 90.9%―100% working load and the servomotor bears only0―9.1% working load. The value of the adjustable-speed and the differential-speed ratio deter-mine the load distribution between the two motors.4.3.3 The output axis running in the decreasing speed region.In the decreasing speed region, the servomotor runs in negative direction, and the range value of K is ?1≤K ≤0 . By eqs. (9) and (10), the P1 is positive, and the P2 is negative. The negative value of the servomotor power shows that the servomotor power is already the working resistance. Hence the conventional motor is not only doing work to the working load, but also doing work to the servomotor power, When the angular speed is in the region 0―n2e, the load of the conventional motor is Thus when the output angular speed is in the decreasing region, the conventional motor consumes more energy than in the other regions. The decrease of the output speed is at the price ofconsuming the servomotor input power. In order to save energy, the output angular speed shouldavoid or reduce running in the decreasing region.4.4 The two drive schemes of the hybrid mechanism of the mechanical pressAccording to eq. (3), the output angular velocity of the hybrid mechanism is equal to the reducedvalue of their sum of the angular velocities of both the conventional motor and the servomotor. Asshown in Figure 1, the output angular velocity of the differential gear train is connected with thecrank axis of the mechanical press, so the two axes have the same angular velocity. When either ofthe conventional motor or the servomotor is driven, or when both of them are driven, the differentangular velocity of the crankshaft of the mechanical press can be obtained. Therefore, two kinds of the schemes of the hybrid mechanism of the mechanical press are proposed: (i) the conventional motor and the servomotor are simultaneously driven; and (ii) the conventional motor and the servomotor are separately driven.4.4.1 The conventional motor and the servomotor being simultaneously driven.This scheme shows that the angular velocity of the crankshaft of the mechanical press is composed of the angular velocity of the conventional motor as the basic speed and the angular velocity of the servomotor as the adjustable speed (Figure 3). The angular velocity and the powers can be calculated by using eqs. (1)―(18).4.4.2 The conventional motor and the servomotor being separately driven. This scheme shows that only one motor is driven in the hybrid input course and at the same time another motor is braked, i.e. when the crankshaft is in differential running stage, the conventional motor and the servomotor are separately operated; thus the different angular velocity of the crankshaft can be obtained. The flexible low speed operation .When the conventional motor is braked and the servomotor is operated, n1 = 0，the below equation can be obtained from eq. (5)Because ?1≤K≤+1 , the output angular velocity of the crankshaft is adjustable and thecrankshaft has two rotating directions; therefore it is flexible. A big value of the drive ratio 1i20 can be designed, so a very small output angular velocity 1 n0 can be achieved. Hence in this course the output angular velocity is flexible and low. When the servomotor is braked and the conventional motor is operated, n2 = 0 , from eq. (5), we have. Crankshaft has two rotating directions; therefore it is flexible. Figure 4 Physical sense of the comparison of the two output angular speed.Because drive ratios 2 i10 and 1 i20 are independent of each other, and the operation and the servomotor operation of the conventional motors are independent of each other too, the values of the two drive ratios can be assigned a very different value (one is very small, and the other is very big), so the two output angular velocities may differ greatly. So doing can satisfy the motion requirements of the mechanical press slide in different stages. The physical sense of comparison of the two output angular speed is illustrated as in Figure 4.5 ConclusionAccording to the velocity characteristics of the mechanical press, the differential gear train is applied in the hybrid mechanism of the mechanical press. Through the above analysis and calculation, the following conclusions can be reached:(1) The adjustable-speed amplitude and differential-speed ratio are important parameters of thehybrid mechanism. They are not only the ratio of the adjustable speed to the basic speed, but alsothe ratio of the power of the servomotor to the power of the conventional motor.(2) With the scheme of the conventional motor and the servomotor being simultaneously driven,the power of the two motors has to be assigned high value in order to satisfy the velocity requirements of the mechanical press. So doing increases the manufacturing cost and the operationcost of the mechanical press, and therefore is valueless in practical application.(3) With the scheme of the conventional motor and the servomotor being separately driven, thepower of the servomotor can be assigned low value in order to satisfy the velocity requirements ofthe mechanical press. So doing decreases the manufacturing cost and the operation cost of themechanical press. Therefore, this scheme proposes a feasible way in practical industrial engineering.中國的科學(xué)系列 E：技術(shù)科學(xué)? 2007 中國科學(xué)出版社施普林格出版社研究利用差動齒輪系實現(xiàn)機械混合壓力何宇鵬，趙勝敦，周軍&張志遠1、 中國，南京 210094，南京大學(xué)科學(xué)與技術(shù)，機械工程學(xué)校2、 中國，西安 710049，西安交通大學(xué)，機械工程學(xué)校本文對機械壓力混合輸入的問題進行了研究，用差動輪系作為傳動機構(gòu)。它建議將“調(diào)速幅度”或“差動速比”作為重要參數(shù)混合投入機械研究中。它不僅規(guī)定了可調(diào)節(jié)幅度速度，而且還決定了伺服電動機功率比的傳統(tǒng)電機。所有傳動軸計算的傳輸功率，兩個電機的功率和工作負載的分布得到了推斷結(jié)果。它提出了伺服電機和傳統(tǒng)電機同時驅(qū)動，伺服電機和傳統(tǒng)電機單獨驅(qū)動兩種驅(qū)動方案。計算結(jié)果表明后者的方案能比伺服電機使用更低的功率，因此這種方案能使得制造和使用成本低得多。后一個方案提出了一個可行的途徑在實際工程中來使用混合機械壓力。機械壓力，混合機制，差動輪系，調(diào)速1、引言目前有許多關(guān)于機械壓力的混合機制的研究報道，并且已經(jīng)成為一個熱門的研究話題?；旌蟿恿C制是一種有 2 個自由度的機制（也稱為差速機制） ，當(dāng)兩個獨立的運動同時輸入時，輸出的運動能夠滿足一些運動要求，這些要求通過機械的運動組成來獲得的?；旌蟿恿C制也可稱為可控機制，或者稱作混合機器。研究機械壓力機的混合機械的目的是使用大功率常規(guī)電機利用飛輪來完成工件的沖壓；并使用低功率的伺服電機來調(diào)整滑塊速度。應(yīng)用在機械壓力中的混合機制的優(yōu)勢在于它不僅可以比伺服壓力機降低更多的制造成本，而且還有一個靈活的工作速度滑塊。所以混合動力機械壓力機在機制上的工作引起了許多研究者的興趣；并且這些研究主要集中在多桿混合機械中。杜和郭已經(jīng)全面討論了七桿的機械壓力機的混合機制，包括組成連桿機構(gòu)的可行條件，滑塊機構(gòu)的動力分析，和兩臺電機之間轉(zhuǎn)矩和功率的分配以及它們之間的優(yōu)化設(shè)計。基于多項式的軌跡規(guī)劃也需要調(diào)查，且計算機模擬表明結(jié)果的確吸引人。此外，孟也調(diào)查了七桿機構(gòu)的運動學(xué)分析，基于最低功率的伺服電機的優(yōu)化設(shè)計已經(jīng)完成，然后孟建議混合機制是機械壓力機的研究方向。Tokuz 首次提出了混合機構(gòu)并且使用差動齒輪系分析了合成速度。他的實驗證實了他的理論的可行性。調(diào)速幅度和差速比的概念在他們的作品中沒有提到，并且兩電機的速度變化和功率之間的關(guān)系也沒有清楚的給出。但是這些概念對混合動力機械選擇兩個電機的功率、決定傳統(tǒng)電機和伺服電機之間的工作負載分配非常重要而且是絕對必要的。在參考文獻[1-3]中他們使用連桿機構(gòu)來實施機械壓力機的混合輸入。這種方法相當(dāng)復(fù)雜，因為連桿機構(gòu)每根連桿的長度和位置的改變會對機械壓力機的滑塊運動產(chǎn)生影響。所以一些主要的問題在混合機械的課程研究中常常被忽略，而且研究結(jié)果不總是和實際工程條件相符合。差動齒輪系有兩個自由度，并且任意兩軸之間的傳動比是一個常數(shù)。為了簡化機械模型并使得問題更加透明，在這篇文章中差速齒輪系常作為傳動機構(gòu)來研究機械壓力機的混合問題。這篇文章討論了兩電機調(diào)速幅度和功率之間的關(guān)系，兩電機之間的工作負載分配，并且提出了傳統(tǒng)電機和伺服電機同時工作、分開工作的兩種驅(qū)動方案。隨著 200 噸的機械壓力機作為工程背景，機械壓力機的混合動力驅(qū)動系統(tǒng)已設(shè)計出來，并且在機械壓力機中的兩種驅(qū)動方案的可行性也已得到了分析。2、混合型機械的主要原則