【正文】 chanical press in this paper. This paper addresses the relationship between the adjustablespeed 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 200ton 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 mechanism The 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 pletely 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 slide The 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 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 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 es 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 mechanism 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 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 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 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. Figure 2 Ideal displacement cure of the slide. The conventional motor’s influence on the output mo