1、 中文 4340 字 出处： Science in China Series E: Technological Sciences February 2007, Volume 50, Issue 1, pp 69-80 Study of utilizing differential gear train to achieve hybrid mechanism of mechanical press HE YuPeng1, ZHAO ShengDun2, ZOU Jun2 & ZHANG ZhiYuan2 1 School of Mechanical Engineering, Nanjing Un
2、iversity of Science & Technology, Nanjing 210094, China； 2 School of Mechanical Engineering, Xian Jiaotong University, Xian 710049, China The problems of hybrid input of mechanical press are studied in this paper, with differential gear train as transmission mechanism. It is proposed that “adjustabl
3、e-speed amplitude” or “differential-speed ratio” is the important parameters for the hybrid input mechanism. It not only defines the amplitude of the adjustable speed, but also determines the ratio of the power of the servomotor to the power of the conventional motor. The calculating equations of th
4、e ratio of transmission in all axes, the power of two motors, and the working load distribution are deduced. The two kinds of driving schemes are put forward that the servomotor and the conventional motor simultaneously drive and the servomotor and the conventional motor separately drive. The calcul
5、ating results demonstrate that the latter scheme can use much lower power of the servomotor, so this scheme makes manufacture and use cost much lower. The latter scheme proposes a feasible way to apply the hybrid mechanism of mechanical press in practice engineering. mechanical press, hybrid mechani
6、sm, differential gear train, adjustable-speed 1 Introduction At present there are many research papers about the hybrid mechanism of mechanical press, and it has become a hot research topic. The hybrid mechanism is a mechanism with 2-degree-of freedom (also called differential speed mechanism), and
7、when two independent motions are input at the same time, the output that can satisfy some motion requirements is obtained through the motion composition of the mechanism. The hybrid mechanism is also called controllable mechanism, or hybrid machine. The purpose of research on hybrid mechanism of mec
8、hanical 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 c
9、ost than servo press, but also has a flexible working velocity of slider1. 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 Guo1, 2 have comprehensively discussed the seven-b
10、ar 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 als
11、o investigated, and the computer simulation shows that the result is indeed attractive. In addition, Meng3 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 th
12、at the hybrid mechanism is a research direction of the mechanical press. Tokuz4 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 amplitu
13、de 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 given5 8. But these concepts are very important and absolutely necessary for the hybrid mechanism to select the two motors power and
14、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 a
15、n 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 conditions9 11. The gear differential train has two freedoms, and the ratios
16、 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 relat
17、ionship 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
18、 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 mechanism The working principle of the hybrid mechanism of the mechanical pres
19、s 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 conn
20、ected 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 con
21、ventional 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 di
22、fferential 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 outp
23、ut 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 ma
24、nufacturing 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 slide The work of the mechanical press presents the regularity of the periodic change12. The displacement and velocity
25、changes of the mechanical press slide in an ideal work circulation are illustrated 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 the working point, its high veloci
26、ty 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 de
27、ad 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 velocit
28、y 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 c
29、enter, and in the other courses it does not do work to the work piece. 4 The nomenclatures and equations of the hybrid mechanism 4.1 The relationship of the angular velocity in all axes There are three external axes in the differential gear train as illustrated in Figure 1. In order to conveniently
30、express the relationship of the three axes, the axis connected with the conventional motor is called axis 1, the axis connected with servomotor is called axis 2, and the axis connected with crankshaft is called axis 0. The angular velocities of the three axes are respectively expressed as n1 , n2 an
31、d 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 that the drive ratio of the other two axes can be determined. So the relationships of drive ratio and angular velocity of the three axes need to be expressed as the character with superscript and subscript.
